Drive transmission device and image forming apparatus including the same

ABSTRACT

A first rotational body 8d and a second rotational body 9a arranged downstream of a driven rotational body 8b in a drive train that transmits a driving force from a driving rotational body 7 to a driven member 4 are included. The first rotational body 8d rotates in synchronization with the driven rotational body 8b. The second rotational body 9a is rotated by the first rotational body 8d and rotates the driven member 4. The first rotational body 8d rotates without rotating the second rotational body 9a when the driven rotational body 8b rotates by an elastic force of an elastic member 11.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/989,650, filed Jan. 6, 2016, which claims the benefit ofInternational Patent Application No. PCT/JP2015/050439, filed Jan. 9,2015, all of which are hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to a drive transmission device thatintermittently transmits drive and an image forming apparatus, such as acopier or a printer, including the drive transmission device.

BACKGROUND ART

In related art, an image forming apparatus includes a configuration thatintermittently transmits a driving force from a drive source. PTL 1discloses a drive transmission device for intermittently driving a sheetfeed roller as a driven member.

The drive transmission device in PTL 1 includes a driving gearconstantly rotated by a motor, and a driven gear that meshes with thedriving gear and rotates, and hence that transmits a driving force tothe sheet feed roller. The driven gear has a toothless portion. Then, byretaining the driven gear with a claw, the driven gear is stopped at aposition, at which the toothless portion faces the driving gear, and thedrive transmission from the driving gear to the driven gear is cut off.By releasing the retention on the driven gear with the claw, the drivengear meshes with the driving gear again and is rotated. With thisconfiguration, the sheet feed roller is intermittently driven.

Also, in PTL 1, when the driven gear is rotated to the position, atwhich the toothless portion faces the driving gear for stopping thedriven gear, or when the stopped driven gear is rotated to the position,at which the driven gear meshes with the driving gear again, thetoothless portion of the driven gear faces the driving gear. Owing tothis, it is difficult to obtain a rotational force from the driving gearand rotate the driven gear. Therefore, in PTL 1, the driven gear isrotated by an elastic force of a tension spring or a leaf spring.

CITATION LIST Patent Literature

PTL 1 Japanese Patent Laid-Open No. 6-50406

However, the configuration in PTL 1 is a drive transmissionconfiguration in which, if the driven gear (a driven rotational body) isrotated, all members from the driven gear to the sheet feed roller asthe driven member constantly rotate. Hence, the tension spring or theleaf spring as an elastic member that rotates the driven gear isrequired to be a configuration that applies a relatively large elasticforce that can rotate all the members from the driven gear to the drivenmember.

If the elastic force of pressing the driven rotational body is large asdescribed above, problems may occur as follows. For example, to generatea large elastic force, an expensive elastic member or a large elasticmember has to be used. This may increase the size and cost of theapparatus. Also, the driven rotational body, the claw that retains thedriven rotational body, or the portion that supports the elastic memberis required to be made of a material in a shape that can resist thelarge elastic force of the elastic member. The apparatus may beincreased in size and cost due to the material and shape.

Also, sound which is generated because the elastic member collides withthe driven rotational body when the elastic member presses the drivenrotational body, and sound which is generated because the drivenrotational body rotated by the elastic member collides with the claw maybe increased by the amount of the large elastic force.

To address the above-described problems, an object of the presentinvention is to decrease the elastic force of the elastic memberrequired for rotating the driven rotational body.

SUMMARY OF INVENTION

Accordingly, the present invention provides a drive transmission deviceincluding a driving rotational body, a driven rotational body thatrotates by engaging with the driving rotational body, a driven memberthat is rotated by the rotation of the driven rotational body, and anelastic member that rotates the driven rotational body by an elasticforce when the driven rotational body does not engage with the drivingrotational body. The drive transmission device includes a firstrotational body and a second rotational body arranged downstream of thedriven rotational body in a drive train that transmits a driving forcefrom the driving rotational body to the driven member, the firstrotational body being configured to rotate in synchronization with thedriven rotational body, the second rotational body being configured tobe rotated by the first rotational body and rotate the driven member.The first rotational body rotates without rotating the second rotationalbody when the driven rotational body rotates by the elastic force of theelastic member.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view of a second transfer unit.

FIG. 1B is a perspective view of the second transfer unit.

FIG. 2A is a perspective view of a first clutch device B1.

FIG. 2B is a perspective view of the first clutch device B1.

FIG. 3A is an illustration of the first clutch device B1 when viewedfrom the front side.

FIG. 3B is an illustration of the first clutch device B1 when viewedfrom the back side.

FIG. 4A is an illustration of the first clutch device B1 when viewedfrom the front side.

FIG. 4B is an illustration of the first clutch device B1 when viewedfrom the back side.

FIG. 5A is an illustration of the first clutch device B1 when viewedfrom the front side.

FIG. 5B is an illustration of the first clutch device B1 when viewedfrom the back side.

FIG. 6A is an illustration of the first clutch device B1 when viewedfrom the front side.

FIG. 6B is an illustration of the first clutch device B1 when viewedfrom the back side.

FIG. 7A is an illustration of the first clutch device B1 when viewedfrom the front side.

FIG. 7B is an illustration of the first clutch device B1 when viewedfrom the back side.

FIG. 8A is a perspective view of a second clutch device B2.

FIG. 8B is a perspective view of the second clutch device B2.

FIG. 9 is a perspective view of the second clutch device B2 beforeassembly.

FIG. 10A is a perspective view explaining assembly of gears 12 and 13.

FIG. 10B is a perspective view explaining assembly of the gears 12 and13.

FIG. 11A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 11B is a cross-sectional view showing play amounts of grooveportions 12 f and key portions 13 h.

FIG. 11C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 12A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 12B is a cross-sectional view showing play amounts of the grooveportions 12 f and the key portions 13 h.

FIG. 12C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 13A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 13B is a cross-sectional view showing play amounts of the grooveportions 12 f and the key portions 13 h.

FIG. 13C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 14A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 14B is a cross-sectional view showing play amounts of the grooveportions 12 f and the key portions 13 h.

FIG. 14C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 15A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 15B is a cross-sectional view showing play amounts of the grooveportions 12 f and the key portions 13 h.

FIG. 15C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 16A is an illustration of the second clutch device B2 when viewedfrom the front side.

FIG. 16B is a cross-sectional view showing play amounts of the grooveportions 12 f and the key portions 13 h.

FIG. 16C is an illustration of the second clutch device B2 when viewedfrom the back side.

FIG. 17 is a schematic cross-sectional view of an image formingapparatus.

FIG. 18 is a perspective view of a third clutch device B3.

FIG. 19A is an illustration showing the third clutch device B3.

FIG. 19B is an illustration showing the third clutch device B3.

FIG. 20A is an illustration showing the third clutch device B3.

FIG. 20B is an illustration showing the third clutch device B3.

FIG. 21A is a perspective view of a drive transmission device DR whenviewed from the front side.

FIG. 21B is a perspective view showing the drive transmission device DRwhen viewed from the back side.

FIG. 22 is a perspective view of the drive transmission device DR beforeassembly.

FIG. 23 is a perspective view showing a configuration of a third clutchsection CL3.

FIG. 24 is a perspective view of the third clutch section CL3 beforeassembly.

FIG. 25A is an explanatory view when the third clutch section CL3 is inan ON state.

FIG. 25B is an explanatory view when the third clutch section CL3 is inan OFF state.

FIG. 26A is an explanatory view of a fourth clutch device B4 when viewedfrom the front side of the drive transmission device DR.

FIG. 26B is an explanatory view of the fourth clutch device B4 whenviewed from the back side of the drive transmission device DR.

FIG. 27A explains assembly of the fourth clutch device B4 when viewedfrom a trigger gear side.

FIG. 27B explains assembly of the fourth clutch device B4 when viewedfrom a driven gear side.

FIG. 28A is a state diagram in which a retained portion 41 c of atrigger gear 41 is retained.

FIG. 28B is a state diagram in which the retention on the retainedportion 41 c of the trigger gear 41 is released.

FIG. 29A is an illustration around the fourth clutch device B4 whenviewed from the front side.

FIG. 29B is an illustration around the fourth clutch device B4 whenviewed from the back side.

FIG. 30A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 30B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 31A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 31B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 32A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 32B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 33A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 33B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 34A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 34B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 35A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 35B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 36A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 36B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 37A is a perspective view around the fourth clutch device B4 whenviewed from the front side.

FIG. 37B is an explanatory view around the fourth clutch device B4 whenviewed from the back side.

FIG. 38 is a schematic cross-sectional view of a color laser beamprinter.

FIG. 39 is an illustration showing a drive transmission configuration toa cartridge.

DESCRIPTION OF EMBODIMENTS

Drive transmission devices according to embodiments of the presentinvention and image forming apparatuses including the drive transmissiondevices are described below.

First Embodiment

Image Forming Apparatus

First, a schematic configuration of an image forming apparatus 100 and aflow of an image forming operation are described with reference to FIG.17.

FIG. 17 is a schematic cross-sectional view showing a generalconfiguration of the color image forming apparatus 100 including imageforming units configured to respectively form images of four colors(yellow Y, magenta M, cyan C, black Bk). The image forming apparatus 100includes, as major members for image formation, a photosensitive drum121, a charging roller 117, a development rotary 123, a belt 102, and afixing unit 125. The photosensitive drum 121, the charging roller 117,and the development rotary 123 serve as toner-image forming means forforming a toner image on the belt 102.

The development rotary 123 rotatably supports a yellow developing unit120Y, a magenta developing unit 120M, a cyan developing unit 120C, and ablack developing unit 120Bk. The yellow developing unit 120Y, themagenta developing unit 120M, the cyan developing unit 120C, and theblack developing unit 120Bk are respectively provided with developingrollers 120YS, 120MS, 120CS, and 120BkS that respectively house tonersof corresponding colors. The belt 102 is an endless belt and woundaround a driving roller 106 and a driven roller 124. The belt 102 is animage bearing body serving as an intermediate transfer body that canbear a toner image on its surface. The driving roller 106 rotates by adriving force from a motor (not shown), rotationally drives the belt102, and hence causes the surface of the belt 102 to move.

An image forming operation on a recording material S is described. Theimage forming apparatus 100 rotates a sheet feed roller 129, hence feedsa sheet of the recording material S in a cassette 128, and convey therecording material S to a registration roller 130. The recordingmaterial S is in a standby state until an image is formed on the belt102 being the endless conveyance belt serving as the intermediatetransfer body rotatable at the position of the registration roller 130.

Meanwhile, the surface of the photosensitive drum 121, which is theimage bearing body that bears the toner image, is uniformly charged withelectricity by the charging roller 117 while the photosensitive drum 121rotates, the surface of the photosensitive drum 121 is exposed to lightby a laser scanner 118 that emits light in accordance with an imagesignal, and hence an electrostatic latent image for an yellow image isformed. The yellow developing unit 120Y houses a toner of yellow, andincludes the developing roller 120YS. By applying a development voltageto the developing roller 120YS facing the photosensitive drum 121 havingthe electrostatic latent image formed thereon, the electrostatic latentimage formed on the photosensitive drum 121 is developed with the tonerof yellow. A voltage with a polarity reverse to the toner image formedon the photosensitive drum 121 is applied to a first transfer roller122, so that the toner image on the photosensitive drum 121 is firsttransferred on the belt 102.

When the toner image of yellow is first transferred on the belt 102, thedevelopment rotary 123 rotates, the magenta developing unit 20M whichexecutes image formation next rotationally moves, and the magentadeveloping unit 20M stops at the development position for imageformation on the photosensitive drum 121. Then, the photosensitive drum121 is charged with electricity and exposed to light similarly to thecase of yellow, a toner image is formed by executing development withthe toner of magenta by the developing roller 120MS, and the toner imageis first transferred on the belt 102. At the first transfer, the tonerimage of magenta is transferred at a position, at which the toner imageof magenta is superposed on the toner image of yellow already born onthe belt 102 (hereinafter, referred to as “overlap transfer”).

Then, similarly to the above-described case, toner images of cyan andblack are formed on the photosensitive drum 121 by using the cyandeveloping unit 120C and the black developing unit 120Bk, and areoverlap transferred on the belt 102. Accordingly, a color toner image,in which the toner images of the four colors including yellow, magenta,cyan, and black are superposed by overlap transfer, is formed on thebelt 102.

After the color image is formed on the belt 102, the recording materialS in the standby state at the registration roller 130 is conveyed to asecond transfer unit A. The second transfer unit A includes a secondtransfer roller 101 that can contact and be separated from the surfaceof the belt 102, and the driving roller 106 (hereinafter, referred to as“counter roller 106”). In a period in which the toner images of therespective colors are overlap transferred on the belt 102 while the belt102 is rotated, the second transfer roller 101 is located at a positionbeing separated from the belt 102 by a gap G (a position indicated by asolid line in FIG. 17) to prevent the toner images already formed on thebelt 102 from being disordered when the toner images pass through thesecond transfer unit A. The second transfer roller 101 moves andcontacts the belt 102 (a position indicated by a broken line in FIG. 17)after the toner images are transferred on the belt 102 and before therecording material S is conveyed to an area between the second transferroller 101 and the belt 102. Then, by applying a voltage with a polarityreverse to the toner to the second transfer roller 101, the toner imageon the belt 102 is transferred on the recording material S being atransferred member, which is pinched and conveyed between the secondtransfer roller 101 and the belt 102.

The recording material S with the toner image transferred from thesurface of the belt 102 is then conveyed to the fixing unit 125, andpasses through a fixing nip portion N between a pressing roller 127 anda fixing roller 126. At this time, the toner image is heated, pressed,and hence fixed to the recording material S. Then, the recordingmaterial S is output onto a sheet output tray 137 at an upper section ofa main body through a sheet output roller 136 so that an image surfacefaces the lower side. The image forming operation is ended.

Second-Transfer-Roller Separate Mechanism

As described above, since the second transfer roller 101 moves atpredetermined timings, and hence contacts and is separated from the belt102, the image forming apparatus 100 includes a contact/separatemechanism of the second transfer roller 101. The contact/separatemechanism is described below.

FIGS. 1A and 1B are perspective views of the second transfer unit A.FIG. 1A shows a state in which the second transfer roller 101 contactsthe belt 102. FIG. 1B shows a state in which the second transfer roller101 is separated from the belt 102. The second transfer roller 101 isrotatably held by a holder 3. While FIGS. 1A and 1B illustrate a firstend portion side in the longitudinal direction of the second transferroller 101, a second end portion side is similarly configured.

A rotating shaft 106 a supported by a frame (not shown) in the imageforming apparatus 100 supports the counter roller 106 and a switch cam 4rotatably around the rotation shaft 106 a. The switch cam 4 has anintegrally formed gear portion 4 a. The gear portion 4 a meshes with aswitch gear 5 rotatably supported at a rotating shaft 5 a. The ratio ofthe number of teeth of the gear portion 4 a to the number of teeth ofthe switch gear 5 is 2:1. By rotating the switch gear 5 by a drivingforce from a motor M through a first clutch device B1, the gear portion4 a and the switch cam 4 are rotated together.

Also, the holder 3 includes a driven roller 3 b. The holder 3 is urged(pressed) in a direction in which the second transfer roller 101approaches the counter roller 106 by a spring 3 a. The switch cam 4rotates by ½ rotation (180 degrees) at a predetermined timing by thefirst clutch device B1, and then the switch cam 4 stops.

In the state shown in FIG. 1B, the driven roller 3 b contacts thesurface of the switch cam 4, hence the position of the second transferroller 101 is restricted, and the second transfer roller 101 isseparated from the belt 102 by the gap G. When the switch cam 4 rotatesby ½ rotation from this state, as shown in FIG. 1A, the surface of theswitch cam 4 is retracted from the driven roller 3 b, and the secondtransfer roller 101 contacts the counter roller 106 by the urging forceof the spring 3 a. When the switch cam 4 is further rotated by ½rotation from this state, the surface of the switch cam 4 contacts thedriven roller 3 b, the driven roller 3 b is moved against the urgingforce (an elastic force) of the spring 3 a, and the second transferroller 101 is separated from the belt 102 by the gap G as shown in FIG.1B. As described above, when the second transfer roller 101 is separatedfrom the contact state with respect to the belt 102, a rotational load(a rotational torque) by the urging force of the spring 3 a is appliedto the switch cam 4.

First Clutch Device B1

Described next is a configuration of the first clutch device B1 as adrive transmission device that is provided in a drive train fortransmitting a driving force from the motor M to the switch cam 4 andthat intermittently transmits the driving force, with reference to FIGS.2A and 2B. FIGS. 2A and 2B are perspective views of the first clutchdevice B1. FIG. 2A is an illustration of the first clutch device B1 whenviewed from the side opposite to the switch gear 5. FIG. 2B is anillustration of the first clutch device B1 when viewed from the side ofthe switch gear 5. Hereinafter, it is assumed that the side opposite tothe switch gear 5 of the first clutch device B1 is “the front side ofthe first clutch device B1,” and the side of the switch gear 5 is “theback side of the first clutch device B1.”

The first clutch device B1 includes a gear 7 (a driving rotational body)that is constantly coupled with the motor M for drive, a gear 8 that canmesh with the gear 7, a gear 9 that can mesh with the gear 8, a solenoid10 being means for restricting rotation of the gear 8, and a torsionspring 11 (an elastic member). The driving force from the motor M istransmitted to the switch gear 5 through the gears 7, 8, and 9 of thefirst clutch device B1, and rotates the switch cam 4 (a driven member).

The gear 8 includes, in an integrally former manner, a retained portion8 a that is retained by a retaining claw 10 a of the solenoid 10, atooth lacking gear 8 b (a driven rotational body) that can mesh with thegear 7, a first slip gear 8 d (a first rotational body) that meshes withthe gear 9, and a cam portion 8 f that contacts the torsion spring 11.When the gear 8 rotates, these retained portion 8 a, tooth lacking gear8 b, gear 8 d, and cam portion 8 f rotate together. The tooth lackinggear 8 b partly has a toothless portion 8 c that does not mesh with thegear 7. The first slip gear 8 d has a tooth-number diametercorresponding to 26 teeth; however, the first slip gear 8 d partly has aslip portion 8 e. The slip portion 8 e has an arcuate surface in aprotruding shape being coaxial with the rotation center of the firstslip gear 8 d and having the same radius as the radius of the pitchcircle of the first slip gear 8 d. Hence, the first slip gear 8 d has 20teeth in a portion other than the slip portion 8 e.

The gear 9 includes, in an integrally formed manner, a second slip gear9 a (a second rotational body) that can mesh with the first slip gear 8d, a shaft 9 c that holds the torsion spring 11, and a rotating shaft 9d integrally coupled with the rotating shaft 5 a of the switch gear 5shown in FIGS. 1A and 1B. When the gear 9 rotates, the second slip gear9 a, the shaft 9 c, and the rotating shaft 9 d are rotated together. Thesecond slip gear 9 a partly has a slip portion 9 b that does not meshwith the first slip gear and extends along the slip portion 8 e. Theslip portion 9 b has an arcuate surface in a recessed shape beingcoaxial with the rotation center of the first slip gear 8 d when theslip portion 9 b is located at a position, at which the slip portion 9 bfaces the slip portion 8 e. The arcuate surface of this slip portion 9 bhas the same radius as the radius of the pitch circle of the first slipgear 8 d, and extends along the arcuate surface of the slip portion 8 e.The gear of the second slip gear 9 a partly has a tooth-number diametercorresponding to 22 teeth; however, the second slip gear 9 a partly hasthe slip portion 9 b. Hence, the second slip gear 9 a has 19 teeth in aportion other than the slip portion 9 b. As described above, the numberof teeth (19 teeth) of the second slip gear 9 a is smaller than thenumber of teeth (20 teeth) of the first slip gear 8 d by one tooth. Toset the gear ratio of the first slip gear 8 d to the second slip gear 9a at 1:1, the second slip gear 9 a has the 19 teeth and an end portion(corresponding to one tooth) of the slip portion 9 b, as a portion thatis pressed and rotated by the 20 teeth of the first slip gear 8 d. Thatis, a relationship of Z1=Z2+1 is satisfied for the gear ratio of 1:1,where Z1 is the number of teeth of the first slip gear 8 d and Z2 is thenumber of teeth of the second slip gear 9 a. Alternatively, the gearratio of the first slip gear 8 d to the second slip gear 9 a is notnecessarily the gear ratio of 1:1. The gear ratio can allow the firstslip gear 8 d to rotate by an integral number of rotations while thesecond slip gear 9 a rotates by one rotation. The slip portion 9 b isarranged at a position, at which the slip portion 9 b faces the slipportion 8 e, every rotation of the first slip gear 8 d. For example, toset the gear ratio at 2:1 (the second slip gear 9 a rotates by ½rotation when the first slip gear 8 d rotates by one rotation) withoutchange in configuration of the first slip gear 8 d, the slip portion 9 bcan be provided every 19 teeth. At this time, a relationship ofZ1=(Z2+1)/2 is satisfied.

The gears 8 and 9 are assembled by aligning their relative rotationphases so that the slip portion 8 e having the arcuate surface in theprotruding shape extends along the slip portion 9 b having the arcuatesurface in the recessed shape. The slip portion 8 e and the slip portion9 b are formed of a material with a small frictional coefficient toallow the slip portion 8 e to easily slide on the slip portion 9 b.Also, to improve the sliding property, a lubricant such as grease may beapplied between the slip portion 8 e and the slip portion 9 b ifrequired.

The solenoid 10 includes the retaining claw 10 a and a return spring 10b. When the return spring 10 b urges the retaining claw 10 a toward thegear 8, the solenoid 10 is not energized, and the retained portion 8 ais located at the position, at which the retained portion 8 a faces theretaining claw 10 a, the retaining claw 10 a can restrict the rotationof the gear 8 by retaining the retained portion 8 a. When the solenoid10 is energized, the retaining claw 10 a is retracted from the gear 8against the urging force of the return spring 10 b. If the retainedportion 8 a is retained by the retaining claw 10 a, the retention on theretained portion 8 a of the gear 8 by the retaining claw 10 a can bereleased.

The torsion spring 11 includes a fixed arm 11 a fixed at a fixingportion (not shown) and a movable arm 11 b that contacts the cam portion8 f of the gear 8, and is held by the shaft 9 c. When the gear 8 is in apredetermined rotation phase, by pressing the cam portion 8 f by theelastic force of the torsion spring 11, the gear 8 is urged to rotate.Even when the toothless portion 8 c of the tooth lacking gear 8 b facesthe gear 7 and hence the tooth lacking gear 8 b cannot obtain asufficient driving force by meshing with the gear 7, the gear 8 can berotated by the pressing with the torsion spring 11.

Operation of First Clutch Device B1

Next, a drive transmission operation of the first clutch device B1 isdescribed with reference to FIGS. 3A to 7B.

Each of FIGS. 3A, 4A, 5A, 6A, and 7A is an illustration of the firstclutch device B1 when viewed from the front side, and each of FIGS. 3B,4B, 5B, 6B, and 7B is an illustration of the first clutch device B1 whenviewed from the back side. FIG. 3 shows the standby state of the firstclutch device B1. FIGS. 4A and 4B show a state at start of drivetransmission of the first clutch device B1. FIGS. 5A and 5B show a stateduring drive transmission of the first clutch device B1. FIGS. 6A and 6Bshow a state at end of drive transmission of the first clutch device B1.FIGS. 7A and 7B shows a state immediately before the gear 8 of the firstclutch device B1 reaches a home position. Also, the rotation directionsof the gears 7 and 8 in FIGS. 3A to 7B are as indicated by arcuatearrows illustrated next to the respective gears.

In the standby state of the first clutch device B1, as shown in FIG. 3A,the toothless portion 8 c of the tooth lacking gear 8 b faces the gear7, and hence the tooth lacking gear 8 b does not mesh with the gear 7.Also, the movable arm 11 b of the torsion spring 11 presses the camportion 8 f so as to rotate the gear 8 clockwise; however, the retainedportion 8 a contacts the retaining claw 10 a. Accordingly, the gear 8 isretained by the retaining claw 10 a, and hence is at a stop withoutrotation. At this time, the gear 8 is at a home position.

Also, as shown in FIG. 3B, the slip portion 8 e of the gear 8 faces theslip portion 9 b of the gear 9. Accordingly, the rotation of the gear 9(the second slip gear 9 a) is restricted and stopped, and hence does notrotate. At this time, the gear 9 is at a home position. When the gear 9is at the home position, since the rotation of the gear 9 is restricted,even if the switch cam 4 or the like is to be rotated by an externalforce or the like, the switch cam 4 is prevented from being rotated.

Next, start of drive transmission of the first clutch device B1 isdescribed. As shown in FIG. 4A, when the solenoid 10 is energized andthe retention on the retained portion 8 a of the gear 8 with theretaining claw 10 a is released, the movable arm 11 b presses the camportion 8 f by the elastic force of the torsion spring 11, the gear 8starts to rotate clockwise, and the tooth lacking gear 8 b meshes withthe gear 7. The cam portion 8 f at this time functions as a pressedsurface that is pressed by the movable arm 11 b of the torsion spring11. When the tooth lacking gear 8 b meshes with the gear 7, the gear 8receives the driving force transmitted from the gear 7, and the gear 8rotates. The gear 8 starts to rotate from the home position only by theelastic force of the torsion spring 11 as described above because thegear 8 cannot mesh with the gear 7 rotating by the motor M while thegear 8 is stopped at the home position.

Also, when the gear 8 starts to rotate, the slip portion 8 e of thefirst slip gear 8 d of the gear 8 slides on the slip portion 9 b of thesecond slip gear 9 a, and hence the gear 8 starts to rotate withoutrotating the gear 9.

When the gear 8 rotates by a predetermined amount without rotating thegear 9 a, as shown in FIG. 4B, a tooth of the first slip gear 8 d nextto an end portion at the upstream side of the slip portion 8 e in therotation direction of the gear 8 engages with an end portion of the slipportion 9 b, and the gear 9 starts to rotate. Accordingly, the teeth ofthe first slip gear 8 d mesh with the teeth of the second slip gear 9 a,the second slip gear 9 a meshes with the first slip gear 8 d, and hencethe gear 9 rotates. When the gear 9 starts to rotate, the switch gear 5starts to rotate, the driving force is transmitted to the switch cam 4through the switch gear 5, and hence the switch cam 4 starts to rotate.

While the gear 8 rotates only by the elastic force of the torsion spring11, the slip portion 8 e of the gear 8 rotates while sliding on the slipportion 9 b of the gear 9, and the gear 9 does not rotate. The timing,at which the gear 9 starts to rotate, is after the timing, at which thetooth lacking gear 8 b meshes with the gear 7, and during a period, inwhich the gear 8 already receives the driving force from the gear 7 androtates. Accordingly, when the driving force is transmitted from thegear 9 to the switch cam 4 to rotate the switch cam 4, the tooth lackinggear 8 b meshes with the gear 7 and the driving force from the motor Mis transmitted to the gear 9.

Thereafter, as shown in FIG. 5A and FIG. 5B, while the gear 8 receivesthe driving force transmitted from the gear 7 and rotates, applicationof electricity to the solenoid 10 is stopped. Accordingly, the retainingclaw 10 a of the solenoid 10 is moved toward the gear 8 by the urgingforce of the return spring 10 b, and the retaining claw 10 a is arrangedat the position, at which the retaining claw 10 a can retain theretained portion 8 a.

Then, as shown in FIG. 6B, when the meshing between the first slip gear8 d and the second slip gear 9 a is ended by the rotation of the gear 8,the slip portion 8 e faces the slip portion 9 b. Accordingly, the gear 9does not receive the driving force transmitted from the gear 8, therotation of the gear 9 is stopped, and the gear 9 is arranged at thehome position again. As described above, the gear 9 is rotated by onerotation by the gear 8, and the rotation of the gear 9 is stopped. Sincethe gear 9 is stopped in this way, the driving force is no longertransmitted to the gear 9 and the drive train arranged downstream of thegear 9, the switch gear 5 and the switch cam 4 are also stopped. At thistime, as shown in FIG. 6A, the tooth lacking gear 8 b still meshes withthe gear 7, and the gear 8 rotates.

Then, by the rotation of the gear 8, the cam portion 8 f presses andmoves the movable arm 11 b of the torsion spring 11 toward the fixed arm11 a against the elastic force. That is, the cam portion 8 f is rotated,the torsion spring 11 is compressed, and the elastic force is increased(charged). The cam portion 8 f at this time functions as a pressingsurface that presses the movable arm 11 b of the torsion spring 11toward the fixed arm 11 a.

Then, as the gear 8 rotates, as shown in FIG. 7A, the toothless portion8 c faces the gear 7, the tooth lacking gear 8 b cannot mesh with thegear 7, and the gear 8 no longer receives the driving force from thegear 7. At this time, if the toothless portion 8 c stops before movingto the position, at which the toothless portion 8 c completely faces thegear 7, sound may be generated by slight collision between the rotatinggear 7 and a tooth tip of the tooth lacking gear 8 b. To avoid this, thegear 8 is further rotated without the driving force from the gear 7. Tobe specific, the cam portion 8 f is pressed by the elastic force of thetorsion spring 11 and the gear 8 is rotated to cause the toothlessportion 8 c to completely face the gear 7 and to cause the teeth of thetooth lacking gear 8 b to be sufficiently retracted from the gear 7 inthe rotation direction of the gear 8. The cam portion 8 f at this timefunctions as a pressed surface that is pressed by the movable arm 11 bof the torsion spring 11. The gear 8 rotates by the elastic force of thetorsion spring 11 until the retained portion 8 a is retained by theretaining claw 10 a of the solenoid 10. When the retained portion 8 a isretained by the retaining claw 10 a, as shown in FIG. 3A, the gear 8 isstopped and is located at the home position.

As shown in FIG. 7B, while the gear 8 is rotated to the home positiononly by the elastic force of the torsion spring 11, the slip portion 8 eof the gear 8 slides on the slip portion 9 b. The gear 8 rotates to thehome position without rotating the gear 9 and stops. This is because theslip portion 8 e of the gear 8 faces the slip portion 9 b of the gear 9before the timing, at which the tooth lacking gear 8 b no longer mesheswith the gear 7, and the driving force of the gear 8 is no longertransmitted to the gear 9.

Then, when the solenoid 10 is energized again and the retaining claw 10a releases the retention on the retained portion 8 a of the gear 8, theabove-described intermittent drive transmission operation is executed.

As described above, when the gear 8 is at the home position, byenergizing the solenoid 10 at a predetermined timing, the first clutchdevice B1 transmits the driving force to rotate the switch gear 5 by onerotation and to rotate the switch cam 4 by ½ rotation.

As described above, in this embodiment, with the first clutch device B1,while the gear 8 cannot obtain the driving force from the gear 7 and thegear 8 is rotated only by the elastic force of the torsion spring 11,the gear 8 is rotatable without rotating the gear 9. That is, in aperiod described below, the gear 8 is rotated only by the elastic forceof the torsion spring 11. The period includes a period from when theretention between the retaining claw 10 a and the retained portion 8 ais released to when the tooth lacking gear 8 b meshes with the gear 7,and a period from when the meshing between the tooth lacking gear 8 band the gear 7 is ended to when the retained portion 8 a is retained bythe retaining claw 10 a. During this period, the slip portion 8 e of thegear 8 faces the slip portion 9 b of the gear 9. The gear 8 is rotatablewithout transmitting the driving force to the gear 9 and the drive trainarranged downstream of the gear 9, and rotating the gear 9 and thedownstream drive train. Hence, the elastic force of the torsion spring11, which is means for rotating the gear 8 when the gear 8 cannot obtainthe driving force from the gear 7, can be merely a force that is largerthan a rotational resistance force of the gear 8.

With the configuration of related art in PTL 1, while the drivenrotational body rotates by the elastic force of the elastic member, allmembers from the driven rotational body to the driven member constantlyrotate. In contrast, in this embodiment, while the driven rotationalbody (the gear 8) rotates by the elastic force of the elastic member(the torsion spring 11), the first rotational body (the first slip gear8 d) rotates without rotating the second rotational body (the secondslip gear 9 a). Accordingly, with the configuration of this embodiment,the elastic force of the elastic member that rotates the drivenrotational body can be smaller than the configuration of related art.

As the result, a small and inexpensive elastic member can be used.Accordingly, the increase in size and cost of the apparatus can beavoided by the amount of reduced size and cost of the elastic member.Also, the driven rotational body, the retaining claw that retains thedriven rotational body, and the portion that supports the elastic memberare not required to employ a material and a shape that resist a largeelastic force. Accordingly, the increase in size and cost can be avoidedwith the shape and material.

Also, the sound which is generated because the elastic member collideswith the driven rotational body when the elastic member presses thedriven rotational body, and the sound which is generated because thedriven rotational body rotated by the elastic member collides with theretaining claw can be decreased by the decreased amount of the elasticforce.

Also, if the apparatus is assembled against the elastic force of theelastic member, the ease of assembly and workability are less degradedby the decreased amount of the elastic force.

Also, when the driven rotational body is rotated while the drivingrotational body meshes with the driven rotational body, the pressingforce of the elastic member serves as a rotational resistance of thedriven rotational body. However, the rotational resistance by thepressing force of the elastic member is decreased by the decreasedamount of the elastic force. Accordingly, the driving force required forthe motor M serving as the drive source for rotating the drivenrotational body can be decreased by the decreased amount of therotational resistance. Accordingly, a low-output, inexpensive, and smalldrive source can be used.

Also, while the gear 9 is at the home position and the gear 8 rotates bythe elastic force of the torsion spring 11, the driving force from themotor M is not transmitted from the first slip gear 8 d to the secondslip gear 9 a. However, the slip portion 8 e and the slip portion 9 bhave the shapes extending along each other, and the rotation of thesecond slip gear 9 a is restricted. Accordingly, even if the drive trainfrom the second slip gear 9 a to the switch cam 4 is to be rotated by anexternal force or the like, the rotation of the drive train isrestricted.

Other Configurations

The configuration described in this embodiment can be modified asfollows.

As long as the rotation of the second slip gear 9 a is restricted by apredetermined amount while the slip portion 8 e of the gear 8 faces theslip portion 9 b of the gear 9, a gap may be present between the arcuatesurfaces of the slip portion 8 e and the slip portion 9 b.

Also, in view of the apparatus configuration, when the gear 9 is at thehome position, if the rotation of the gear 9 is not required to berestricted, the first slip gear 8 d can be rotatable without rotatingthe second slip gear 9 a while the slip portion 8 e faces the slipportion 9 b.

Also, in this embodiment, the tooth lacking gear 8 b and the first slipgear 8 d are integrally molded and coaxially rotate. However, the toothlacking gear 8 b and the first slip gear 8 d may rotate around differentaxes. That is, the first slip gear 8 d can be located downstream of thetooth lacking gear 8 b in the drive train from the motor M to the switchcam 4. Similarly, the switch gear 5 and the second slip gear 9 a are notrequired to be coaxial, and the switch gear 5 can be located downstreamof the second slip gear 9 a in the drive train from the motor M to theswitch cam 4.

Also, in this embodiment, the driving force is transmitted by themeshing of the gears; however, in a case of a configuration thattransmits a driving force by rotation, a friction wheel or the like maybe used.

Also, the first clutch device B1 of this embodiment is used for drivingthe contact/separate mechanism of the second transfer roller 101;however, the first clutch device B1 can be applied to another mechanism.For example, the first clutch device B1 can be applied to anintermittent rotation mechanism of the sheet feed roller 129, and apressure release mechanism between the pressing roller 127 and thefixing roller 126. Also, in a case of an in-line image forming apparatusincluding a plurality of photosensitive drums, the first clutch deviceB1 can be applied to a contact/separate mechanism of a first transferroller and a contact/separate mechanism of a developing roller. Further,the first clutch device B1 can be applied to a mechanism that turns ONand OFF transmission of a driving force from the drive source, and amechanism that turns ON and OFF transmission of a driving force from thedrive source to the photosensitive drum.

Second Embodiment

Second Clutch Device B2

Next, a second clutch device B2 as a drive transmission device accordingto a second embodiment of the present invention is described withreference to FIGS. 8A, 8B, 9, 10A, and 10B.

FIGS. 8A and 8B are perspective views of the second clutch device B2according to the second embodiment. FIG. 8B is a perspective view of thesecond clutch device B2 when viewed from the side facing the switch gear5 in FIGS. 1A and 1B. FIG. 8A is a perspective view of the clutch devicewhen viewed from the side opposite to FIG. 8B. FIG. 9 is a perspectiveview of the second clutch device B2 before assembly. FIGS. 10A and 10Bare perspective views explaining assembly of a gear 12 and a gear 13.FIG. 10A is an illustration viewed from the gear 13 side, and FIG. 10Bis an illustration viewed from the gear 12 side. Similar reference signsare applied to configurations similar to those in the above-describedfirst embodiment, and the description is omitted.

The second clutch device B2 transmits the driving force from the motor Mto the switch gear 5 similarly to the first clutch device B1 of thefirst embodiment. The second clutch device B2 differs from the firstclutch device B1 in that the second clutch device B2 includes the gear13 corresponding to the gear 8 of the first clutch device B1, and inaddition, the gear 12 for rotating the gear 13 so that the gear 13 at ahome position can mesh with the gear 7.

First, a configuration of the second clutch device B2 is described. Thegears 7 and 9 are similar to those of the first clutch device B1, andhence the description is omitted.

The gear 12 includes, in an integrated manner, a trigger gear 12 b thatmeshes with the gear 7, a retained portion 12 a that is retained by theretaining claw 10 a of the solenoid 10 and rotation is restricted, and aboss 12 d arranged with a trigger spring 14. The trigger gear 12 bpartly has a toothless portion 12 c that does not mesh with the gear 7.

The gear 13 includes, an integrated manner, a tooth lacking gear 13 athat can mesh with the gear 7, a first slip gear 13 c that meshes withthe gear 9, a cam portion 13 e that contacts the torsion spring 11 andapplies an urging force to the gear 13 to rotate the gear 13, a boss 13f arranged with the trigger spring 14, and a rotating shaft portion 13g. The tooth lacking gear 13 a partly has a toothless portion 13 b thatdoes not mesh with the gear 7. The first slip gear 13 c partly has aslip portion 13 d. The slip portion 13 d has a pitch-circle diameter ofa protruding shape being an arcuate surface with the same radius as theradius of the pitch circle of the first slip gear 8 d. Also, the gear ofthe first slip gear 13 c has a tooth-number diameter corresponding to 26teeth; however, a tooth portion forming the first slip gear 13 c isformed of 20 teeth.

The retaining claw 10 a of the solenoid 10 can restrict rotation of thegear 12 by retaining the retained portion 12 a of the gear 12.

A first end of the trigger spring 14 is fixed to the boss 12 d of thegear 12, and a second end of the trigger spring 14 is fixed to the boss13 f of the gear 13. The trigger spring 14 urges the gear 12 and thegear 13 in a direction in which the gear 12 is attracted to the gear 13.Also, when the solenoid 10 is energized and the retaining claw 10 areleases the retention on the retained portion 12 a of the gear 12, thetrigger spring 14 applies a rotation starting force to the gear 12, andthe trigger gear 12 b meshes with the gear 7.

The fixed arm 11 a side of the torsion spring 11 is fixed, and themovable arm 11 b side of the torsion spring 11 contacts the cam portion13 e of the gear 13 and urges the cam portion 13 e toward the center ofthe rotating shaft portion 13 g of the gear 13.

Next, arrangement of the gear 12 and the gear 13 is described. As shownin FIG. 10A and FIG. 10B, the gear 12 has a bearing portion 12 e and aplurality of groove portions 12 f. The bearing portion 12 e is housed onthe rotating shaft portion 13 g of the gear 13. At this time, aplurality of key portions 13 h of the gear 13 are housed in the grooveportions 12 f. In a state in which the key portions 13 h are housed inthe groove portions 12 f, plays are provided between the key portions 13h and the groove portions 12 f. The gear 12 can rotate relative to thegear 13 around the rotating shaft portion 13 g by the amounts of theplays.

Operation of Second Clutch Device B2

Next, a drive transmission operation of the clutch device according tothe second embodiment is described with reference to FIGS. 11A to 16C.Each of FIGS. 11A, 12A, 13A, 14A, 15A, and 16A is an illustration of thesecond clutch device B2 when viewed from the front side (the switch gear5 side), each of FIGS. 11B, 12B, 13B, 14B, 15B, and 16B is across-sectional view showing play amounts between the groove portions 12f of the gear 12 and the key portions 13 h of the gear 13 of the secondclutch device B2 when viewed from the front side (the switch gear 5side), and each of FIGS. 11C, 12C, 13C, 14C, 15C, and 16C is anillustration of the second clutch device B2 when viewed from the backside (the side opposite to the switch gear 5 side). FIGS. 11A to 11Cshow a standby state of the second clutch device B2. FIGS. 12A to 12Cshow a state at start of rotation of the gear 12 of the second clutchdevice B2. FIGS. 13A to 13C show a state at start of drive transmissionof the second clutch device B2. FIGS. 14A to 14C are explanatory viewsof a state during drive transmission of the second clutch device B2.FIGS. 15A to 15C show a state at end of drive transmission of the secondclutch device B2. FIGS. 16A to 16C show a state immediately before thegear 13 reaches a home position.

In the standby state of the second clutch device B2, as shown in FIG.11B, the movable arm 11 b contacts a flat portion of the cam portion 13e, and urges the flat portion toward the center of the rotating shaftportion 13 g of the gear 13. In this state, the gear 13 is at a homeposition, and the toothless portion 13 b faces the gear 7. Accordingly,the driving force from the gear 7 is not transmitted to the gear 13.Also, plays are provided between the groove portions 12 f and the keyportions 13 h.

Also, as shown in FIG. 11A, the gear 12 is urged by the trigger spring14 to rotate clockwise. However, the retained portion 12 a of the gear12 is retained by the retaining claw 10 a and hence the gear 12 is at astop. In this state, the toothless portion 12 c is at a home position,at which the toothless portion 12 c faces the gear 7. The driving forceof the gear 7 is not transmitted to the gear 12.

Also, as shown in FIG. 11C, the slip portion 13 d of the gear 13contacts the slip portion 9 b of the gear 9. In this state, the rotationof the gear 9 is restricted. Even if the rotating shaft 9 d being anoutput target of the driving force receives a rotational torque from theoutput target, the gear 9 cannot be rotated. At this time, the gear 9 isat a home position.

Then, to execute drive transmission by the second clutch device B2, thegear 12 is rotated first. Accordingly, as shown in FIG. 12A, thesolenoid 10 is energized, hence the retaining claw 10 a is retractedfrom the gear 12, and the retention on the retained portion 12 a by theretaining claw 10 a is released. Then, the boss 12 d of the gear 12 ismoved toward the boss 13 f of the gear 13 by the elastic force of thetrigger spring 14, and the gear 12 starts to rotate clockwise. At thistime, since the cam portion 13 e is pressed by the torsion spring 11,the rotation of the gear 13 is restricted. Accordingly, the gear 13 doesnot rotate even if the gear 13 receives the elastic force of the triggerspring 14. When the gear 12 rotates by a predetermined amount, thetrigger gear 12 b meshes with the gear 7, the gear 12 receives thedriving force from the gear 7, and the gear 12 rotates.

Also, as shown in FIG. 12B, when the gear 12 rotates by the triggerspring, the gear 13 is held at the standby position by the pressingforce of the torsion spring 11 until the plays between the grooveportions 12 f and the key portions 13 h are used up by the rotation ofthe gear 12. Accordingly, as shown in FIG. 12C, while the gear 13 is ata stop, the slip portion 13 d of the gear 13 contacts the slip portion 9b of the gear 9 similarly to FIG. 11C, and the gear 9 stops at the homeposition without rotating.

When the trigger gear 12 b meshes with the gear 7, the gear 12 receivesthe driving force from the gear 7, and the gear 12 rotates as shown inFIG. 13A, the plays between the groove portions 12 f and the keyportions 13 h are used up as shown in FIG. 13B, and edge portions of thegroove portions 12 f press the key portions 13 h. Accordingly, the gear13 starts to rotate. Then, the tooth lacking gear 13 a of the gear 13meshes with the gear 7, and the driving force is transmitted from thegear 7 to the gear 13.

After the retention on the retained portion 12 a is released and thegear 12 rotates, application of electricity to the solenoid 10 isstopped as shown in FIG. 13A. Accordingly, the retaining claw 10 a movestoward the gear 12 by the return spring 10 b, and the retaining claw 10a causes the retained portion 12 a to be brought into the standby stateat the position, at which the retaining claw 10 a can retain theretained portion 12 a.

Also, when the gear 13 starts to rotate, the slip portion 13 d of thefirst slip gear 13 c slides on the slip portion 9 b of the second slipgear 9 a, and hence the gear 13 starts to rotate without rotating thegear 9.

When the gear 13 rotates by a predetermined amount without rotating thegear 9 a, as shown in FIG. 13C, a tooth of the first slip gear 13 c nextto an end portion at the upstream side of the slip portion 13 d in therotation direction of the gear 13 engages with an end portion of theslip portion 9 b, and the gear 9 starts to rotate. Accordingly, a toothof the first slip gear 13 c bites into a tooth of the second slip gear 9a, the second slip gear 9 a meshes with the first slip gear 13 c, andhence the gear 9 rotates.

When the gear 9 starts to rotate, the switch gear 5 starts to rotate,the driving force is transmitted to the switch cam 4 through the switchgear 5, and hence the switch cam 4 starts to rotate.

Then, as shown in FIG. 14A, the trigger gear 12 b of the gear 12 mesheswith the gear 7 and the gear 12 rotates. As shown in FIG. 14B, the toothlacking gear 13 a of the gear 13 meshes with the gear 7 and the gear 13rotates. Also, as shown in FIG. 14C, the second slip gear 9 a of thegear 9 meshes with the first slip gear 13 c of the gear 13 and rotates.Accordingly, the switch gear 5 rotates, and the switch cam 4 rotates. Asdescribed above, when the driving force is transmitted from the gear 9to the switch cam 4 to rotate the switch cam 4, the gear 13 meshes withthe gear 7 and the driving force from the motor M is transmitted to thegear 9.

Immediately before the gear 12 rotates by one rotation, as shown in FIG.15A, since the toothless portion 12 c of the trigger gear 12 b faces thegear 7 and the trigger gear 12 b does not mesh with the gear 7, the gear12 no longer receives the driving force from the gear 7. At this time,also as shown in FIG. 15B, since the gear 13 meshes with the gear 7 androtates, the boss 13 f of the gear 13 presses the boss 12 d through thetrigger spring 14 with a natural length, and hence the gear 12 rotates.Then, when the gear 12 rotates by one rotation, the retained portion 12a contacts the retaining claw 10 a and is retained. Accordingly, thegear 12 stops at the home position.

Also, as shown in FIG. 15B, while the gear 13 meshes with the gear 7 androtates, the cam portion 13 e presses the movable arm 11 b against theelastic force of the torsion spring 11, compresses the torsion spring11, and charges the elastic force.

Since the plays are provided again between the groove portions 12 f andthe key portions 13 h when the gear 12 is retained by the retaining claw10 a and stops, the gear 13 is rotatable by a predetermined amount whilethe gear 12 stops.

Also, as shown in FIG. 15C, while the gear 13 meshes with the gear 7 androtates, the meshing between the first slip gear 13 c and the secondslip gear 9 a is ended by the rotation of the gear 13, and the slipportion 13 d faces the slip portion 9 b. Accordingly, the gear 9 doesnot receive the driving force transmitted from the gear 13, the rotationof the gear 9 is stopped, and the gear 9 is arranged at the homeposition again. As described above, the gear 9 is rotated by onerotation by the gear 13, and the rotation of the gear 9 is stopped.Since the gear 9 stops in this way, the driving force is no longertransmitted to the gear 9 and the drive train arranged downstream of thegear 9, the switch gear 5 and the switch cam 4 also stop.

Then, the gear 13 receives the driving force from the gear 7 androtates. At this time, since the gear 12 is at a stop, the key portions13 h move in the groove portions 12 f. Then, as shown in FIG. 16B, thetoothless portion 13 b faces the gear 7, the tooth lacking gear 13 acannot mesh with the gear 7, and the gear 13 no longer receives thedriving force from the gear 7. At this time, if the toothless portion 13b stops before moving to the position, at which the toothless portion 13a completely faces the gear 7, sound may be generated by slightcollision between the rotating gear 7 and a tooth tip of the toothlacking gear 13 a. To avoid this, the gear 13 is further rotated withoutthe driving force from the gear 7. To be specific, the gear 13 isrotated by pressing the cam portion 13 e by the elastic force of thetorsion spring 11, so that the toothless portion 13 b completely facesthe gear 7 and the teeth of the tooth lacking gear 13 b are sufficientlyretracted from the gear 7 in the rotation direction of the gear 13. Thegear 13 rotates to a position, at which the gear 13 is no longer rotatedby the pressure on the cam portion 13 e with the movable arm 11 b due tothe elastic force of the torsion spring 11, and the gear 13 stops.Accordingly, the gear 13 is located at the home position shown in FIG.11B. The position, at which the gear 13 no longer rotates by thepressure on the cam portion 13 e with the movable arm 11 b due to theelastic force of the torsion spring 11, is a position at which themovable arm 11 b contacts the flat portion of the cam portion 13 e andhence the pressing force of the movable arm 11 b does not act as arotational moment of the gear 13.

Also, while the gear 13 rotates in the state in which the rotation ofthe gear 12 stops (while the key portions 13 h move in the grooveportions 12 f), the boss 13 f of the gear 13 moves away from the boss 12d of the gear 12. Accordingly, the trigger spring 14 is expanded and theelastic force is charged. Accordingly, as shown in FIGS. 12A to 12C,when the retention on the retained portion 12 a by the retaining claw 10a is released, the gear 12 can be rotated.

Also, as shown in FIG. 16C, while the gear 13 is rotated to the homeposition only by the elastic force of the torsion spring 11, the slipportion 13 d of the gear 13 slides on the slip portion 9 b. The gear 13rotates to the home position without rotating the gear 9 and stops. Thisis because the slip portion 13 d of the gear 13 faces the slip portion 9b of the gear 9 before the timing at which the tooth lacking gear 13 ano longer meshes with the gear 7, and the driving force of the gear 13is no longer transmitted to the gear 9.

With this embodiment, in the second clutch device B2, while the gear 13cannot obtain the driving force from the gear 7 and the gear 13 isrotated only by the elastic force of the torsion spring 11, the gear 13is rotatable without rotating the gear 9. That is, in a period from whenthe meshing between the tooth lacking gear 13 a and the gear 7 is endedto when the gear 13 stops, the gear 13 is rotated only by the elasticforce of the torsion spring 11. During this period, the slip portion 13d of the gear 13 faces the slip portion 9 b of the gear 9. The gear 13is rotatable without transmitting the driving force to the gear 9 andthe drive train arranged downstream of the gear 9, and rotating the gear9 and the downstream drive train.

Accordingly, the elastic force of the torsion spring 11 that rotates thegear 13 when the gear 13 cannot obtain the driving force from the gear 7can be merely a force that is larger than the total sum of a rotationalresistance force of the gear 13, such as a frictional force, and a forceof rotating the gear 13 by a predetermined amount against the elasticforce of the trigger spring 14. Accordingly, as compared with theconfiguration of related art described in PTL 1 and the like, theelastic force of the torsion spring 11 can be decreased. Similarly tothe first embodiment, the increase in size and cost of the apparatus canbe avoided. Also, the sound which is generated because the elasticmember collides with the driven rotational body when the elastic memberpresses the driven rotational body, and the sound which is generatedbecause the driven rotational body rotated by the elastic membercollides with the retaining claw can be decreased.

Also, the ease of assembly and workability are less degraded, and thedriving force required for the drive source (the motor M) can bedecreased. Accordingly, a low-output, inexpensive, and small drivesource can be used.

Also, while the gear 9 is at the home position and the gear 13 rotatesby the elastic force of the torsion spring 11, even if the drive trainfrom the second slip gear 9 a to the switch cam 4 is to be rotated by anexternal force or the like, the rotation of the drive train isrestricted.

The configuration of the above-described embodiment can be modified intoother configurations similar to those described in the first embodiment.

Third Embodiment

Third Clutch Device B3

Next, a third clutch device B3 as a drive transmission device accordingto a third embodiment of the present invention is described withreference to FIGS. 18, 19A, 19B, 20A, and 20B. Similar reference signsare applied to configurations similar to those in the above-describedfirst embodiment, and the description is omitted. FIG. 18 is anillustration explaining overview of the third clutch device B3. Thethird clutch device B3 is provided in a drive train through which thedriving force from the motor M is transmitted, and includes a firstclutch section CL1, and a second clutch section CL2 that receives thedriving force transmitted from the first clutch section CL1 andtransmits the driving force to the switch gear 5.

The configuration of the second clutch section CL2 is similar to thefirst slip gear 8 d and gear 9 according to the first embodiment.

The first clutch section CL1 includes an input gear 701 integrallyformed with a drive transmission claw (a driving rotational body) 705,an output gear (a driven rotational body) 702, a pressing lever 703, anda solenoid SL. The input gear 701 is rotated by a gear 707 that rotateswhen receiving the driving force transmitted from the motor M. Also, thedriving force is transmitted from the output gear 702, through a gear708 and an idler gear (not shown), to the first slip gear 8 d of thesecond clutch section CL2. The first slip gear 8 d rotates insynchronization with the output gear 702. The gear ratio of the outputgear 702 to the first slip gear 8 d is 1:1.

The input gear 701 and the output gear 702 are rotated togethercoaxially around a rotation center 709. The output gear 702 holds adrive transmission lever (an engagement member) 704 that can engage withthe drive transmission claw 705. The drive transmission lever 704 heldby the output gear 702 swings around a shaft 702 a different from therotation center 709. The drive transmission lever 704 is movable betweena position at which the drive transmission lever 704 engages with thedrive transmission claw 705 and a position at which the drivetransmission lever 704 is retracted from the drive transmission claw 705and does not engage with the drive transmission claw 705. A cam portion706 having a cam surface 706 a is integrally formed on the outerperiphery of the output gear 702. The pressing lever (a pressing member)703 being pulled by a spring 711 presses the cam surface 706 a, andhence the pressing lever 703 applies a rotational force to the outputgear 702. The cam portion is rotatable together with the output gear702.

Operation of Third Clutch Device B3

Next, a drive transmission operation of the third clutch device B3 isdescribed with reference to FIGS. 19A to 20B which are illustrations ofthe drive transmission device when viewed from the axial direction ofthe rotation center 709.

In a standby state of the third clutch device B3, as shown in FIG. 19A,the solenoid SL is not energized, and a flapper 207 being a retainingmember that retains the drive transmission lever 704 retains the drivetransmission lever 704 in the first clutch section CL1. At this time,the drive transmission lever 704 is at an engagement release position atwhich the engagement between the drive transmission claw 705 and thedrive transmission lever 704 is released. Accordingly, drive is nottransmitted from the input gear 701 to the output gear 702, the outputgear 702 stops at a home position, and only gears, such as the inputgear 701 and the gear 707, arranged at the upstream side in the drivetransmission direction rotate. The input gear 701 rotates in an arrow Cdirection.

At this time, in the second clutch section CL2, the first slip gear 8 dand the gear 9 are at a stop in a state similar to that shown in FIG.3B.

Next, start of drive transmission of the third clutch device B3 isdescribed. In the first clutch section CL1, the solenoid SL isenergized, the flapper 207 is retracted from the drive transmissionlever 704, and the retention between the drive transmission lever 704and the flapper 207 is released. Then, a spring 710 provided between theoutput gear 702 and the drive transmission lever 704 presses the drivetransmission lever 704 to turn the drive transmission lever 704 in anarrow D1 direction. The drive transmission lever 704 moves to theengagement position and engages with the drive transmission claw 705.With this engagement, as shown in FIG. 19B, the input gear 701 and theoutput gear 702 are coupled to each other through the drive transmissionlever 704, the input gear 701 and the output gear 702 start to rotatetogether in the arrow C direction, and the driving force is transmittedfrom the output gear 702 to the drive output gear 708. The reason thatthe spring 710 presses the drive transmission lever 704 is describedlater.

At this time, in the second clutch section CL2, the first slip gear 8 dand the gear 9 are at a stop in a state similar to that shown in FIG.4B.

Then, in the first clutch section CL1, the input gear 701 and the outputgear 702 are coupled to each other and rotate together in the arrow Cdirection. During this period, application of electricity to thesolenoid SL is stopped, and the retracted flapper 207 is in a staterestored to a retention position at which the flapper 207 can retain thedrive transmission lever 704.

At this time, in the second clutch section CL2, the first slip gear 8 dand the gear 9 mesh with each other and rotate in a state similar tothat shown in FIG. 5B.

Then, immediately before the output gear 702 rotates substantially byone rotation from the home position, as shown in FIG. 6B, the meshingbetween the first slip gear 8 d and the second slip gear 9 a is ended,and the slip portion 8 e faces the slip portion 9 b. Accordingly, thegear 9 does not receive the driving force transmitted from the firstslip gear 8 d, the rotation of the gear 9 is stopped, and the gear 9 isarranged at the home position again. As described above, the gear 9 isrotated by one rotation by the first slip gear 8 d, and the rotation ofthe gear 9 is stopped. Since the gear 9 stops in this way, the drivingforce is no longer transmitted to the drive train of the gear 9 andother components arranged downstream of the gear 9, the switch gear 5and the switch cam 4 also stop. At this time, in the first clutchsection CL1, the output gear 702 and the input gear 701 are coupled toeach other and rotate together.

Then, in the first clutch section CL1, as shown in FIG. 20A, when thedrive transmission lever 704 rotating together with the output gear 702is returned to the position at which the drive transmission lever 704contacts the flapper 207, a first end portion 704 a of the drivetransmission lever 704 is retained by the flapper 207. Since a secondend portion 704 b of the drive transmission lever 704 engages with thedrive transmission claw 705 at an instance when the first end portion704 a contacts the flapper 207, the drive transmission lever 704 ispulled by the drive transmission claw 705. Accordingly, the drivetransmission lever 704 turns in a C2 direction around the first endportion 704 a, which contacts the flapper 207, as a support point untilthe engagement between the second end portion 704 b and the drivetransmission claw 705 is released. When the engagement is released, thedriving force is no longer transmitted from the drive transmission claw705 to the output gear 702. When the output gear 702 stops at this time,the drive transmission lever 704 cannot be further retracted from thedrive transmission claw 705. Hence, at the time when the output gear 702stops, the drive transmission lever 704 may be in a state in which thedrive transmission lever 704 is not retracted by a sufficient distancefrom the drive transmission claw 705. In this situation, the second endportion 704 b of the drive transmission lever 704 may collide with a tipend of the continuously rotating drive transmission claw 705 and soundmay be generated, resulting in generation of noise.

Therefore, in this embodiment, as shown in FIG. 20B, the pressing lever703 being urged by the spring 711 presses the cam surface 706 a of thecam portion 706, applies the rotational force to the output gear 702,and rotates the output gear 702. Then, by the rotation of the outputgear 702, the drive transmission lever 704 is retracted from the drivetransmission claw 705 by a sufficient distance. The pressing lever 703can turn around a shaft 703 a.

To be more specific, in the state in which the first end portion 704 aof the drive transmission lever 704 contacts the flapper 207, and thesecond end portion 704 b of the drive transmission lever 704 engageswith the drive transmission claw 705, a tip end of the pressing lever703 presses an inclined portion L of the cam surface 706 a in an arrow Edirection. By pressing the inclined portion L of the cam surface 706 aas described above, the rotational force is applied to the output gear702 and the output gear 702 is rotated in the C direction. By therotation of the output gear 702, the shaft 702 a also rotates in the Cdirection around the rotation center 709. With this rotational force,the drive transmission lever 704 is turned in the D2 direction aroundthe first end portion 704 a serving as the support point. Even after theengagement between the second end portion 704 b and the drivetransmission claw 705 is released, the drive transmission lever 704 isfurther turned in the D2 direction. Accordingly, the second end portion704 b of the drive transmission lever 704 can be retracted from thedrive transmission claw 705 by a sufficient distance.

The length and inclination of the inclined portion L of the cam surface706 a is set so that the rotation of the output gear 702 is stopped atthe home position being a proper position at which the second endportion 704 b of the drive transmission lever 704 is at a sufficientdistance from the drive transmission claw 705.

In this way, the drive transmission lever 704 is retracted from thedrive transmission claw 705. When this retraction operation of the drivetransmission lever 704 is viewed from the output gear 702, the drivetransmission lever 704 rotates around the shaft 702 a so that the secondend portion 704 b is separated from the drive transmission claw 705. Atthis time, the drive transmission lever 704 presses and compresses thespring 710 while turning. Hence, when the output gear 702 stops, thespring 710 is in a pressed and compressed state. When the flapper 207releases the retention on the drive transmission lever 704, the spring710 is released as described above, and the spring 710 presses and turnsthe drive transmission lever 704.

As described above, while the pressing lever 703 presses the cam portion706 by the elastic force of the spring 711 and hence the output gear 702is rotated to the home position in the first clutch section CL1, thesecond clutch section CL2 is in a state similar to that shown in FIG.7B. That is, the first slip gear 8 d rotates without rotating the gear9. This is because the slip portion 8 e of the first slip gear 8 d facesthe slip portion 9 b of the gear 9 before the timing at which the drivetransmission lever 704 is retracted from the drive transmission claw705, and the driving force of the first slip gear 8 d is no longertransmitted to the gear 9.

As described above, in this embodiment, while the output gear 702 cannotobtain the driving force from the drive transmission claw 705 and theoutput gear 702 is rotated by pressing the cam portion 706 with thepressing lever 703 due to the elastic force of the spring 711 in thefirst clutch section CL1, the first slip gear 8 d is rotatable withoutrotating the gear 9 in the second clutch section CL2. That is, in aperiod from when the engagement between the drive transmission lever 704and the drive transmission claw 705 of the output gear 702 is releasedto when the output gear 702 stops, the output gear 702 is rotated onlyby the elastic force of the spring 711. During this period, the slipportion 8 e of the first slip gear 8 d faces the slip portion 9 b of thegear 9. The first slip gear 8 d is rotatable without transmitting thedriving force to the gear 9 and the drive train arranged downstream ofthe gear 9, and rotating the gear 9 and the downstream drive train.

Hence, the elastic force of the spring 711 for rotating the output gear702 when the output gear 702 cannot obtain the driving force from thedrive transmission claw 705 can be merely a force that is larger than arotational resistance force of the drive train from the output gear 702to the first slip gear 8 d, such as a frictional force. Accordingly, theelastic force of the spring 711 can be decreased, and the increase insize and cost of the apparatus can be avoided similarly to the firstembodiment. Also, the sound which is generated because the elasticmember collides with the driven rotational body when the elastic memberpresses the driven rotational body, and the sound which is generatedbecause the driven rotational body rotated by the elastic membercollides with the retaining claw can be decreased.

Also, the ease of assembly and workability are less degraded, and thedriving force required for the drive source (the motor M) can bedecreased. Accordingly, a low-output, inexpensive, and small drivesource can be used.

Also, while the gear 9 is at the home position and the output gear 702rotates by the elastic force of the torsion spring 711, even if thedrive train from the second slip gear 9 a to the switch cam 4 is to berotated by an external force or the like, the rotation of the drivetrain is restricted.

The configuration of the above-described embodiment can be modified intoother configurations similar to those described in the first embodiment.

Fourth Embodiment

Next, a drive transmission device DR according to a fourth embodiment ofthe present invention, and an image forming apparatus 200 including thedrive transmission device DR are described.

Image Forming Apparatus

First, a schematic configuration of the image forming apparatusaccording to this embodiment and a flow of an image forming operationare described with reference to FIG. 38.

FIG. 38 is a schematic cross-sectional view showing a generalconfiguration of a full-color laser beam printer 200 (hereinafter,referred to as “image forming apparatus 200”) including image formingunits configured to respectively form images of four colors (yellow Y,magenta M, cyan C, black Bk).

As shown in FIG. 38, the image forming apparatus 200 includes fourcartridges 201 (201Y, 201M, 201C, 201B) arranged in parallel in thehorizontal direction. The cartridges 201 are integrally provided withphotosensitive drums 202 (202Y, 202M, 202C, 202B) as image bearingbodies, charging rollers 203 (203Y, 203M, 203C, 203B) respectivelyarranged around the photosensitive drums 202 and configured torespectively uniformly charge the surfaces of the photosensitive drum202 with electricity, and developing rollers 204 (204Y, 204M, 204C,204B) as developing members that respectively cause toners to adhere tothe photosensitive drums 202 and develop the toners as toner images.Also, toners with predetermined colors (not shown) are respectivelyhoused in the cartridges 201. The toners are respectively supplied tothe surfaces of the developing rollers 204 by rotation of supply rollers205 (205Y, 205M, 205C, 205B).

A belt 206 is an endless-belt-shaped image bearing body that is woundaround a driving roller 206 a, a driven roller 206 b, and a tensionroller 206 c. The belt 206 serves as an intermediate transfer body thatcan bear toner images on its surface. Also, the belt 206 is rotationallydriven when the driving roller 206 a rotates counterclockwise, and thesurface of the belt 206 is moved.

Four first transfer rollers 206 d and a cleaning device 227 are arrangedaround the belt 206. The first transfer rollers 206 d are arranged atpositions at which the first transfer rollers 206 d respectively facethe photosensitive drums 202, and respectively transfer the toner imageson the surface of the photosensitive drums 202 onto the belt 206. Thecleaning device 227 removes a transfer remaining toner remaining on thesurface of the belt 206.

An image forming operation on a recording material S is described. Theimage forming apparatus 200 rotates a sheet feed roller 208counterclockwise, hence feeds sheets of the recording material S in acassette 209 one by one, and conveys the recording material S to aregistration roller 210. The recording material S is conveyed to asecond transfer roller 211, in synchronization with a formationoperation of toner images to be formed on the surface of the belt 206,by using the registration roller 210.

Meanwhile, in synchronization with the operation of feeding therecording material S, the photosensitive drums 202 are uniformly chargedwith electricity by the charging rollers 203 while rotating clockwise.Further, the photosensitive drums 202 are exposed to light by laserscanners 212 (212Y, 212M, 212C, 212B) that emit light in accordance withimage signals while the photosensitive drums 202 rotate clockwise, andelectrostatic latent images are formed.

The electrostatic latent images of the photosensitive drum 202 aredeveloped by the developing rollers 204 and hence are visualized astoner images. The photosensitive drums 202 contact the belt 206, and thetoner images on the surfaces of the photosensitive drums 202 aresequentially transferred by overlap transfer on the belt 206 by thefirst transfer rollers 206 d.

Then, the toner image developed in an overlap manner on the belt 206 ismoved together with the belt 206 to the driving roller 206 a and thesecond transfer roller 211, and then the toner image is secondtransferred on the recording material S. The toner image transferred onthe recording material S is conveyed to a fixing roller pair 213 beingtoner fixing means. The toner image is heated and pressed, and hence isfixed to the recording material S when passing through a nip portion ofthe fixing roller pair 213. Then, the recording material S is outputonto a sheet output tray 215 at an upper section of the image formingapparatus 200 through a sheet output roller pair 214 so that a tonerimage surface faces the lower side. The image forming operation isended.

In the following description, a configuration of the cartridge 201B anda drive transmission configuration to the cartridge 201B are described.However, this description can be similarly applied to the othercartridges 201Y, 201M, and 201C.

Cartridge Driving Configuration

Next, a method of driving the photosensitive drum 202 and the developingroller 204 in the cartridge 201 is described with reference to FIG. 39.FIG. 39 is an illustration showing the drive transmission configurationto the cartridge 201B of black Bk. FIG. 39 includes a cartridge 201Bportion illustrated in a perspective view, and a drive transmissiondevice DR portion illustrated in a conceptual diagram.

As shown in FIG. 39, the cartridge 201B includes a support shaft 216that supports the developing roller 204B so that the developing roller204B can swing relative to the photosensitive drum 202B, a pressurespring 217, and a rib 218. The developing roller 204B is urged tocontact the photosensitive drum 202B by the pressure spring 217 aroundthe support shaft 216 as the rotation center. In the cartridge 201B, thedeveloping roller 204B contacts the photosensitive drum 202B during theimage forming operation, and the developing roller 204B is separatedfrom the photosensitive drum 202B in a situation other than the imageforming operation. The contact state of the developing roller 204B withthe photosensitive drum 202B is held by an urging force of the pressurespring 217. When the developing roller 204B is separated from thephotosensitive drum 202B, the rib 218 is pressed, moved, and fixed by acontact/separate mechanism (not shown) in a direction against the urgingforce of the pressure spring 217. Accordingly, the separated state ofthe developing roller 204B from the photosensitive drum 202 is held.

A drum coupling member 219B and a development coupling member 220B arerespectively provided at end portions of the rotating shafts of thephotosensitive drum 202B and the developing roller 204B. The othercartridges 201Y, 201M, and 201C are configured similarly to theabove-described cartridge 201B.

The cartridge 201B obtains a driving force from a motor MB being a drivesource. The other cartridges 201Y, 201M, and 201C are also provided withcorresponding motors. A rotational force output from the motor MB isdivided into a drum driving shaft D1 and a development driving shaft D2(described later), the drum driving shaft D1 engages with the drumcoupling member 219B, and the rotational force drives the photosensitivedrum 202B. Also, the development driving shaft D2 engages with thedevelopment coupling member 220B, and hence the rotational force drivesthe developing roller 204B.

In the middle of the drive transmission from the motor MB to thedevelopment driving shaft D2, a fourth clutch device B4 and a thirdclutch section CL3 (described later) are arranged. By operating thefourth clutch device B4 at a predetermined timing, the third clutchsection CL3 is switched between a drive transmission state (hereinafter,referred to as ON state) and a drive cut-off state (hereinafter,referred to as OFF state). By the switching between the drivetransmission state and the drive cut-off state, switching betweenrotation and stop of the development driving shaft D2 is provided. Whenthe developing roller 204B contacts the photosensitive drum 202B, thefourth clutch device B4 operates the third clutch section CL3 totransmit the driving force of the motor MB to the development drivingshaft D2, so that the developing roller 204B is rotated. Also, when thedeveloping roller 204B is separated from the photosensitive drum 202B,the third clutch section CL3 is operated to cut off the driving force ofthe motor MB to the development driving shaft D2, so that the rotationof the developing roller 204B is stopped.

Drive Transmission to Drum

The configuration of transmitting the driving force from the motor MB tothe driving shaft D1 and the driving shaft D2 is described withreference to FIGS. 21A, 21B, and 22. FIG. 21A and FIG. 21B areperspective views of the drive transmission device DR. FIG. 21A is anillustration of the drive transmission device DR when viewed from thecartridge 201B. FIG. 21B is an illustration of the drive transmissiondevice DR when viewed from a side opposite to the cartridge 201B.Hereinafter, it is assumed that the cartridge 201B side of the drivetransmission device DR is “the front side of the drive transmissiondevice DR” and the side opposite to the cartridge 201B is “the back sideof the drive transmission device DR.” FIG. 22 is a perspective view ofthe drive transmission device DR before assembly.

The drive transmission device DR includes a motor MB being a drivesource, a drum gear 21, and the above-described drum driving shaft D1.The drum driving shaft D1 is coaxially coupled to the drum gear 21. Amotor shaft MB1 meshes with the drum gear 21. Drive from the motor MBrotates the drum driving shaft D1 through the motor shaft MB1 and thenthe drum gear 21. Accordingly, when the drum driving shaft D1 engageswith a drum coupling member 19B and the motor MB rotates, the drum 202Bconstantly rotates.

Drive Transmission to Developing Roller

Next, a configuration that transmits the driving force from the motor MBto the development driving shaft D2 is described. The drive transmissiondevice DR includes a first idler gear 22 that can mesh with the drumgear 21, and the third clutch section CL3 having a clutch gear 23 thatcan mesh with the first idler gear 22. The third clutch section CL3includes the driving shaft D2 that can engage with the developmentcoupling member 220B as described above. Accordingly, drive from themotor MB constantly rotates the first idler gear 22 and the clutch gear23 from the motor shaft MB1 through the drum gear 21.

When the development driving shaft D2 engages with the developmentcoupling member 220B and the third clutch section CL3 is in the ONstate, the driving force of the clutch gear 23 rotates the developmentdriving shaft D2, and rotates the development coupling member 220B and adeveloping roller 204B. In contrast, when the third clutch section CL3is in the OFF state, the development driving shaft D2 does not rotate,and the development coupling member 220B or the developing roller 204Bdoes not rotate.

The switching between the ON state and the OFF state of the third clutchsection CL3 is executed by moving a slide member 31 by the fourth clutchdevice B4. A second idler gear 24 that can mesh with the first idlergear 22, a third idler gear 25 that can mesh with the second idler gear24, and the fourth clutch device B4 that can mesh with the third idlergear 25 are arranged downstream of drive of the first idler gear 22 ofthe drive transmission device DR. The third idler gear 25 being adriving rotational body has a gear portion 25 a that meshes with thesecond idler gear 24, and a gear portion 25 b that can mesh with thefourth clutch device B4. The third idler gear 25 constantly rotateswhile the motor MB rotates. The fourth clutch device B4 includes asecond slip gear 30 that can mesh with a first slip gear 29 and isrotatable coaxially with the third idler gear 25. Further, the slidemember 31 that makes a slide motion by rotation of the second slip gear30, and a slide spring 32 that urges the slide member 31. The slidespring 32 has a fixed end 32 a fixed to a fixing portion (not shown),and an operation end 32 b arranged in a housing portion 31 a of theslide member 31. The slide spring 32 urges the slide member 31 in adirection from the fixed end 32 a to the operation end 32 b. By rotationof the second slip gear 30 of the fourth clutch device B4, the slidemember 31 makes the slide motion (reciprocating movement), and hence thethird clutch section CL3 is alternately switched between the ON stateand the OFF state. That is, the fourth clutch device B4 is a drive trainfor moving the slide member 31.

Configuration of Third Clutch Section CL3

First, a configuration of the third clutch section CL3 is described withreference to FIGS. 23 and 24. FIG. 23 is a perspective view showing theconfiguration of the third clutch section CL3. FIG. 24 is a perspectiveview of the third clutch section CL3 before assembly. The developmentdriving shaft D2 has a plurality of engagement portions D2 a that engagewith the development coupling member 220B. A parallel pin 37 is arrangedin a hole D2 b of the development driving shaft D2. The clutch gear 23that meshes with the first idler gear 22 being a driving rotational bodyis rotatable relative to the development driving shaft D2, and theposition of the clutch gear 23 is determined in the axial direction. Theinside of the clutch gear 23 is hollowed. An inner peripheral portion ofa slide boss 23 a near the center serves as a slide surface forpositioning in the axial direction and for rotation relative to thedevelopment driving shaft D2 at the driven side. An outer peripheralportion of the slide boss 23 a serves as a slide surface for positioningin the axial direction and for rotation of a driving engagement member33. Four rotation stoppers 23 b are provided at the inside of the clutchgear 23. The rotation stoppers 23 b serve as rotation stoppers for thedriving engagement member 33.

An inner peripheral surface of the driving engagement member 33 isfitted on the outer peripheral portion of the slide boss 23 a of theclutch gear 23. Accordingly, the driving engagement member 33 issupported so that the driving engagement member 33 can slide. Then, whenrotation stoppers 33 a provided on an outer peripheral portion mesh withthe rotation stoppers 23 b of the clutch gear 23, the driving engagementmember 33 rotates together with the clutch gear 23. Also, fourprotrusions 33 b are provided at the driving engagement member 33. Theprotrusions 33 b mesh with protrusions 34 a of a driven engagementmember 34. Accordingly, the rotational force is transmitted to thedriven engagement member 34. Surfaces of the protrusions 33 b of thedriving engagement member 33 meshing with the protrusions 34 a areinclined in a direction in which the meshing surfaces bite into acounter part by rotation. Accordingly, even when the third clutchsection CL3 is in the ON state, the meshing is reliably provided, andeven when a large torque is applied, jumping does not occur. Also,portions between the protrusions 33 b of the driving engagement member33 are connected by gentle inclined surfaces 33 c. Accordingly, evenwhen the third clutch section CL3 is changed from the OFF state to theON state during rotation, the engagement can be smoothly provided.

A slide portion 33 d that rotationally slides on a release member 35 isprovided at an end surface at the driven engagement member 34 side ofthe driving engagement member 33. Also, the driving engagement member 33is constantly urged by a coil spring 36 serving as an elastic membertoward the driven engagement member 34. The development driving shaft D2is fitted into the inner peripheral surface of the driven engagementmember 34, and the parallel pin 37 is fitted into a groove 34 b of thedriven engagement member 34. Also, the driven engagement member 34 hasfour protrusions 34 a. When the protrusions 34 a mesh with theprotrusions 33 b of the driving engagement member 33, the rotationalforce is transmitted. Surfaces of the protrusions 34 a meshing with theprotrusions 33 b of the driving engagement member 33 are inclined in abiting direction similarly to the protrusions 33 b of the counter part.Also, the protrusions 34 a of the driven engagement member 34 areconnected by gentle inclined surfaces 34 c. The driving engagementmember 33, the driven engagement member 34, and the coil spring 36 areprovided inside the clutch gear 23. With this configuration, the spacecan be effectively used and the configuration can be compact. Also, therotational force transmitted from the tooth surface can be directlytransmitted. Accordingly, a force of twisting or tilting is notgenerated at the engagement member, the part strength is likely ensured,and a large torque can be transmitted.

The release member 35, a lever member 38, and a bearing 39 are providedcoaxially with the development driving shaft D2. A rotation stopperportion 39 a of the bearing 39 is fixed by a fixing member (not shown),and hence rotation is restricted. The release member 35 has a pluralityof guide portions 35 a. The guide portions 35 a are fitted into a holeportion 39 b of the bearing 39. Accordingly, the release member 35 ismovable in the axial direction while its rotation is restricted relativeto the development driving shaft D2. Also, the release member 35 has acontact portion 35 b that contacts the slide portion 33 d of the drivingengagement member 33 and causes the release member 35 to move in theaxial direction, and a pressed portion 35 c that is pressed by the levermember 38.

The lever member 38 is provided rotatably relative to the bearing 39.The lever member 38 has a lever engagement portion 38 a that engageswith a slide engagement portion 31 b provided at the slide member 31,and a pressing portion 38 b that contacts the pressed portion 35 c ofthe release member 35. The lever member 38 turns when the slide member31 makes the slide motion. A plurality of the pressed portions 35 c ofthe release member 35 are provided symmetrically to the axis center anda plurality of the pressing portions 38 b of the lever member 38 areprovided symmetrically to the axis center.

Description on Operation of Third Clutch Section CL3

An operation of the third clutch section CL3 is described with referenceto FIGS. 25A and 25B. FIG. 25A is an explanatory view of the ON state ofthe third clutch section CL3. FIG. 25B is an explanatory view of the OFFstate. As shown in FIG. 25A, in a state in which the pressing portions38 b of the lever member 38 do not contact the pressed portions 35 c ofthe release member 35, the release member 35 is pressed in a directionopposite to the clutch gear 23 by an elastic force of a coil spring 36.Accordingly, the driving engagement member 33 is pressed by the drivenengagement member 34, and is brought into a meshing state (not shown).Accordingly, the rotational force from the motor MB is transmitted fromthe clutch gear 23 to the development driving shaft D2, that is, thestate becomes the ON state.

In contrast, as shown in FIG. 25B, when the slide member 31 slides in adirection in which the slide member 31 compresses the slide spring 32,the lever member 38 turns counterclockwise. Accordingly, the pressingportions 38 b of the lever member 38 contact the pressed portions 35 cof the release member 35. The release member 35 is pushed and moved inthe axial direction of the development driving shaft D2. Accordingly,the contact portion 35 b of the release member 35 contacts the slideportion 33 d of the driving engagement member 33, and the drivingengagement member 33 is separated from the driven engagement member 34against the urging force of the coil spring 36. Accordingly, therotational force from the motor MB is not transmitted from the clutchgear 23 to the development driving shaft D2, that is, the state becomesthe OFF state.

In this case, a load resistance when the lever member 38 is turned isthe largest in the OFF state in which the coil spring 36 is the mostcompressed, by the influence of the elastic force of the coil spring 36.In contrast, in the ON state, since the elastic force of the coil spring36 is used for pressing the driving engagement member 33 to the drivenengagement member 34, the load resistance when the lever member 38 isturned is as small as a rotational sliding load between the lever member38 and the bearing 39. Accordingly, the urging force of the slide spring32 for restoring the slide member 31 to the position in the ON state isa larger urging force than the load resistance when the lever member 38in the OFF state is moved.

Configuration of Fourth Clutch Device B4

Next, a configuration of the fourth clutch device B4 is described withreference to FIG. 26A, FIG. 26B, FIG. 27A, FIG. 27B, FIG. 28A, FIG. 28B,FIG. 29A, and FIG. 29B. FIG. 26A is an explanatory view of the fourthclutch device B4 when viewed from the front side of the drivetransmission device DR, and FIG. 26B is an explanatory view of thefourth clutch device B4 when viewed from the back side of the drivetransmission device DR. FIG. 27A and FIG. 27B are perspective viewsexplaining assembly of the fourth clutch device B4. Each of FIGS. 26A,27A, 28A, and 29A is an illustration viewed from the trigger gear side.Each of FIGS. 26B, 27B, 28B, and 29B is an illustration viewed from thedriven gear side.

The fourth clutch device B4 includes a driven gear 40 and a trigger gear41 that can mesh with the gear portion 25 b of the third idler gear (adriving rotational body) 25. The fourth clutch device B4 is arranged onthe axis of a rotating shaft 29 a of the first slip gear 29.

A solenoid 26 that controls the operation of the fourth clutch deviceB4, a spring support shaft 27, and a torsion spring 28 (an elasticmember) are arranged near the fourth clutch device B4. The driven gear(a driven rotational body) 40 includes, in an integrated manner, twodriven gear portions 40 a, two driven toothless portions 40 b, a camportion 40 c, a boss 40 d, a slide shaft portion 40 e, an engagementportion 40 f, and key portions 40 g. The two driven gear portions 40 acan mesh with the gear portion 25 b of the third idler gear 25. The twodriven toothless portions 40 b are portions that do not mesh with thegear portion 25 b provided at part of the driven gear portions 40 a. Thetorsion spring 28 contacts the cam portion 40 c, and the cam portion 40c causes an urging force to be applied to the driven gear 40 and causesthe driven gear 40 to be rotated. The boss 40 d is provided with atrigger spring 42. The engagement portion 40 f engages with the firstslip gear. Also, the driven gear portions 40 a are symmetricallyprovided about the center of the rotating shaft of the driven gear 40,and the driven toothless portions 40 b are symmetrically provided aboutthe center of the rotation shaft of the driven gear 40. The gear of thedriven gear portions 40 a has a tooth-number diameter corresponding to36 teeth. Tooth portions forming the driven gear portions 40 a each have15 teeth. The driven toothless portions 40 b each have a sizecorresponding to 3 teeth of each of the driven gear portions 40 a.

The trigger gear (another driven rotational body) 41 includes, in anintegrated manner, two trigger gear portions 41 a, two trigger toothlessportions 41 b, two retained portions 41 c, housing portions 41 d, aslide surface 41 e, and claws 41 f. The two trigger gear portions 41 acan mesh with the gear portion 25 b of the third idler gear 25. The twotrigger toothless portions 41 b are portions that do not mesh with thegear portion 25 b provided at part of the trigger gear portions 41 a.The two retained portions 41 c are retained by a retaining claw 26 a ofthe solenoid 26. The housing portions 41 d house the trigger spring 42.The slide surface 41 e is rotationally supported by the slide shaftportion 40 e of the driven gear 40. The claws 41 f position the drivengear 40 in the axial direction. Also, the trigger gear portions 41 a aresymmetrically provided about the center of the rotating shaft of thetrigger gear 41. The trigger toothless portions 41 b are symmetricallyprovided about the center of the rotating shaft of the trigger gear 41.The retained portions 41 c are symmetrically provided about the centerof the rotating shaft of the trigger gear 41. The gear of the triggergear portions 41 a has a tooth-number diameter corresponding to 36teeth. Tooth portions forming the trigger gear portions 41 a each have15 teeth. The trigger toothless portions 41 b each have a sizecorresponding to 3 teeth of each of the trigger gear portions 41 a. Whenthe trigger gear 41 is arranged at the driven gear 40 by the claws 41 f,the key portions 40 g of the driven gear 40 are housed in the housingportions 41 d of the trigger gear 41. In a state in which the keyportions 40 g are housed in the housing portions 41 d, plays areprovided between the key portions 40 g and the housing portions 41 d.The trigger gear 41 can rotate relative to the driven gear 40 around thecenter of the rotating shaft by the amounts of the plays.

The solenoid 26 includes the retaining claw 26 a and a return spring 26b. When the return spring 26 b urges the retaining claw 26 a toward thetrigger gear 41, the solenoid 26 is not energized, and one of theretained portions 41 c is located at the position at which the retainedportion 41 c faces the retaining claw 26 a, the retaining claw 26 a canrestrict the rotation of the trigger gear 41 by retaining the retainedportion 41 c. When the solenoid 26 is energized, the retaining claw 26 ais retracted from the trigger gear 41 against the urging force of thereturn spring 26 b. If the retained portion 41 c is retained by theretaining claw 26 a until then, the retention on the retained portion 41c of the trigger gear 41 by the retaining claw 26 a can be released.

A first end of the trigger spring 42 is fixed to the boss 40 d of thedriven gear 40, and a second end of the trigger spring 42 is housed inone of the housing portions 41 d of the trigger gear 41. The triggerspring 42 urges the trigger gear in a direction in which the triggergear is separated from the driven gear 40 in the rotation direction.Also, when the solenoid 26 is energized and the retaining claw 26 areleases the retention on the retained portion 41 c of the trigger gear41, the trigger spring 42 applies a rotation starting force to thetrigger gear 41, and one of the trigger gear portions 41 a meshes withthe gear portion 25 b.

The torsion spring 28 includes a fixed arm 28 a fixed at a fixingportion (not shown) and a movable arm 28 b that contacts the cam portionof the driven gear, and the torsion spring 28 is held by the springsupport shaft 27. When the driven gear 40 is in a predetermined rotationphase, by pressing the cam portion 40 c of the driven gear 40 by theelastic force of the torsion spring 28, the driven gear 40 is urged torotate. Even when one of the driven toothless portions 40 b of thedriven gear 40 faces the gear portion 25 b of the third idler gear 25and the driven gear 40 cannot obtain a sufficient driving force from thethird idler gear 25, the driven gear 40 can be rotated by the pressureof the torsion spring 28.

The first slip gear (a first rotational body) 29 includes engagementportions 29 b and a first slip portion 29 d. The engagement portions 29b engage with the engagement portion 40 f of the driven gear 40. Thefirst slip portion 29 d does not have a first gear portion 29 c (a firstrotational body) or a gear portion. The first slip portion 29 d has apitch-circle diameter of a protruding shape being an arcuate surfacewith the same radius as the radius of the pitch circle of the first gearportion 29 c. The first slip gear 29 is coupled coaxially by theengagement portions 29 b and the engagement portion 40 f of the drivengear 40. When the driven gear 40 meshes with the third idler gear 25 androtates, the first slip gear 29 rotates together. Also, the gear of thefirst slip gear 29 has a tooth-number diameter corresponding to 16teeth. A tooth portion forming the first gear portion 29 c has 11 teeth.The first slip portion 29 d has a size corresponding to 5 teeth of thefirst gear portion 29 c.

Next, arrangement of the trigger gear 41 and the driven gear 40 isdescribed with reference to FIGS. 28A and 28B. FIG. 28A is a statediagram in which one of the retained portions 41 c of the trigger gear41 is retained, and FIG. 28B is a state diagram in which the retentionon the retained portion 41 c of the trigger gear 41 is released. Asshown in FIG. 28A, in a state in which the retaining claw 26 a retainsthe retained portion 41 c of the trigger gear 41, the rotation of thetrigger gear 41 is restricted, and the trigger gear portions 41 a andthe trigger toothless portions 41 b are respectively arranged in thesame phases as the phases of the driven gear portions 40 a and thedriven toothless portions 40 b. As shown in FIG. 28B, when the solenoid26 is energized and the retaining claw 26 a releases the retention onthe retained portion 41 c, the trigger gear 41 rotates clockwise by arotation starting force of the trigger spring 42 (not shown). In thisembodiment, as the above-described amounts of the plays between the keyportions 40 g and the housing portion 41 d, the gears of the triggergear portions 41 a are rotated relative to the gears of the driven gearportions 40 a by the amount of 3 teeth.

The second slip gear 30 and the slide member 31 are described withreference to FIGS. 29A and 29B. FIG. 29A is an illustration around thefourth clutch device B4 when viewed from the front side, and FIG. 29B isan explanatory view around the fourth clutch device B4 when viewed fromthe back side. A component not required for description is notillustrated for easier description on the configuration. The second slipgear (a second rotational body) 30 has three second gear portions 30 a(second rotational bodies) that can mesh with the first gear portion 29c of the first slip gear 29, and three second slip portions 30 b that donot have a gear portion and hence do not mesh with the first gearportion 29 c. The second slip portions 30 b each have an arcuate surfacein a recessed shape being coaxial with the rotation center of the firstslip gear 29 when one of the second slip portions 30 b is located at aposition at which the second slip portion 30 b faces one of the firstslip portions 29 d. The arcuate surface has the same radius as thepitch-circle radius of the first gear portion 29 c.

The second gear portions 30 a are provided in equal phases about therotation center of the second slip gear 30. The second slip portions 30b are provided in equal phases about the rotation center of the secondslip gear 30. The gear of the second slip gear 30 has a tooth-numberdiameter corresponding to 39 teeth. Tooth portions forming the secondgear portions 30 a each have 10 teeth. The second slip portions 30 beach have a size corresponding to 3 teeth of the second gear portions 30a. As described above, the number of teeth (10 teeth) of each secondgear portion 30 a is smaller than the number of teeth (11 teeth) of thefirst gear portion 29 c by one tooth. The first slip gear 29 and thesecond slip gear 30 are assembled by aligning their relative rotationphases so that the first slip portion 29 d having the arcuate surface inthe protruding shape extends along each of the second slip portions 30 bhaving the arcuate surfaces in the recessed shapes.

The first slip gear 29 and the second slip gear 30 are formed of amaterial with a small frictional coefficient to allow the first slipportion 29 d to slide on each second slip portion 30 b. Also, to improvethe sliding property, a lubricant such as grease may be applied betweenthe first slip portion 29 d and the second slip portions 30 b ifrequired. Also, the second slip gear 30 has three bosses 30 c in equalphases about the rotation center. The slide member 31 makes a slidemotion by rotation of the second slip gear 30. The slide member (adriven member) 31 has the engagement portion 31 b that engages with thelever member 38 of the third clutch section CL3, and a contact portion31 c that contacts the second slip gear 30. The slide member 31 is amovable member that is guided by a guide member (not shown) and isarranged so as to slide back and forth in the longitudinal direction ofthe slide member 31. Also, the slide member 31 is urged by the slidespring 32 in a direction in which the contact portion 31 c contacts oneof the bosses 30 c of the second slip gear 30. When the contact portion31 c does not contact the boss 30 c, the third clutch section CL3 ischanged to the ON state from the OFF state by the urging force.

Description on Operation of Drive Transmission Device

Next, an operation of the drive transmission device DR is described withreference to FIGS. 30A to 37B. Each of FIGS. 30A, 31A, 32A, 33A, 34A,35A, 36A, and 37A is a perspective view around the fourth clutch deviceB4 when viewed from the front side, and each of FIGS. 30B, 31B, 32B,33B, 34B, 35B, 36B, and 37B is an explanatory illustration around thefourth clutch device B4 when viewed from the back side. FIGS. 30A and30B show a first standby state of the fourth clutch device B4. FIGS. 31Aand 31B shows rotation start of the trigger gear of the fourth clutchdevice B4. FIGS. 32A and 32B shows a drive transmission state of thefourth clutch device B4. FIGS. 33A and 33B shows state immediatelybefore drive transmission end of the fourth clutch device B4. FIGS. 34Aand 34B shows a second standby state of the fourth clutch device B4.FIGS. 35A and 35B shows the drive transmission state shifted from thesecond standby state of the fourth clutch device B4. FIGS. 36A and 36Bshows the drive transmission end state shifted from the second standbystate and then from the drive transmission state of the fourth clutchdevice B4. FIGS. 37A and 37B shows a state immediately before the drivengear reaches a home position, from the drive transmission shifted fromthe second standby state of the fourth clutch device B4. Also, therotation directions of respective components in FIGS. 30A to 37B are asindicated by arcuate arrows illustrated next to the respectivecomponents.

In the first standby state of the fourth clutch device B4, as shown inFIG. 30A, the movable arm 28 b contacts a flat portion of the camportion 40 c, and urges the flat portion toward the center of therotating shaft of the driven gear 40. In this state, the pressing forceof the movable arm 28 b does not act as a rotational moment of thedriven gear 40 and hence the driven gear 40 is at the home position.Also, the driven toothless portion 40 b faces the gear portion 25 b.Accordingly, the driving force is not transmitted from the gear portion25 b to the driven gear 40. Also, in the first standby state of thefourth clutch device B4, as shown in FIG. 28A described above, thetrigger gear 41 is urged by the trigger spring 42 to rotate clockwise;however, the retaining claw 26 a retains the retained portion 41 c andhence the trigger gear 41 is at a stop. At this time, the triggertoothless portion 41 b is also at the home position at which the triggertoothless portion 41 b faces the gear portion 25 b. The driving force ofthe gear portion 25 b is not transmitted to the trigger gear 41.

The slide member 31 slides by the boss 30 c in a direction in which theslide spring 32 is compressed, and the position of the slide member 31is fixed at a first position. With this state of the slide member 31,the lever member 38 is turned to a position at which the third clutchsection CL3 becomes the OFF state. Also, as shown in FIG. 30B, the firstslip portion 29 d contacts the second slip portion 30 b. In this state,since the rotation of the second slip gear 30 is restricted, even whenthe second slip gear 30 receives the rotational torque from the slidemember 31 due to the urging force of the slide spring 32, the secondslip gear 30 cannot be rotated. This state is a state in which thesecond slip gear 30 is at the home position. The home position (a stopphase) of the second slip gear 30 when the third clutch section CL3 isin the OFF state and the first slip portion 29 d contacts the secondslip portion 30 b is hereinafter called OFF home position (a first stopphase) of the second slip gear 30.

Then, to execute drive transmission by the fourth clutch device B4, thetrigger gear 41 is rotated first. To rotate the trigger gear 41, asshown in FIG. 31B, the solenoid 26 is energized, hence the retainingclaw 26 a is retracted from the retained portion 41 c, and the retentionon the retained portion 41 c by the retaining claw 26 a is released.Then, as shown in FIG. 28B described above, the trigger gear 41 startsto rotate clockwise by the elastic force of the trigger spring 42. Atthis time, the cam portion 40 c of the driven gear 40 is pressed by themovable arm 28 b. The rotation of the driven gear 40 is restricted andhence the driven gear 40 does not rotate.

When the trigger gear 41 rotates by a predetermined amount, as shown inFIG. 31B, the trigger gear portion 41 a meshes with the gear portion 25b, the trigger gear 41 receives the driving force from the gear portion25 b, and hence the trigger gear 41 rotates. The driven gear 40 is heldat the home position by the pressing force of the movable arm 28 b untilthe trigger gear portion 41 a of the trigger gear 41 rotates by theamount of 3 teeth relative to the gear of the driven gear portion 40 aas shown in FIG. 28B. Accordingly, the first slip gear 29 or the secondslip gear 30 is not rotated while the driven gear 40 is at a stop.

In the drive transmission state of the fourth clutch device B4, as shownin FIG. 32A, when the trigger gear portion 41 a rotates by the amount of3 teeth relative to the gear of the driven gear portion 40 a, the drivengear 40 starts to rotate. Then, the driven gear portion 40 a meshes withthe gear portion 25 b, and the driving force is transmitted from thegear portion 25 b to the driven gear 40. Also, when the driven gear 40starts to rotate, the first slip portion 29 d rotates relative to thesecond slip portion 30 b in a sliding manner while the first slip gear29 does not rotate the second slip gear 30.

When the first slip gear 29 rotates by a predetermined amount, as shownin FIG. 32B, a tooth of the first gear portion 29 c arranged next to adownstream-side end portion of the first slip portion 29 d in therotation direction of the first slip gear 29 engages with an end portionof the second slip portion 30 b and starts the rotation of the secondslip gear 30. Accordingly, the first gear portion 29 c meshes with thesecond gear portion 30 a, and the second slip gear 30 rotatescounterclockwise. At this time, in the second slip gear 30, the boss 30c and the contact portion 31 c are rotated in a sliding manner, and theslide member 31 does not slide.

After the retention on the retained portion 41 c is released and thedriven gear 40 rotates, application of electricity to the solenoid 26 isstopped. Accordingly, the retaining claw 26 a moves toward the triggergear 41 by the return spring 26 b, and the retaining claw 26 a isbrought into the standby state in which the retaining claw 26 a canretain the retained portion 41 c. Also, while the driven gear 40 mesheswith the gear portion 25 b and rotates, the cam portion 40 c presses themovable arm 28 b against the elastic force of the torsion spring 28,compresses the torsion spring 28, and charges the elastic force.

Immediately before the end of drive transmission of the fourth clutchdevice B4, as shown in FIG. 33B, the retained portion 41 c of thetrigger gear 41 is retained by the retaining claw 26 a, and the rotationis stopped at the home position. Also, with the rotation of the secondslip gear 30, the boss 30 c is separated from the contact portion 31 c,the slide member 31 slides by the urging force of the slide spring 32 ina direction in which the slide spring 32 is expanded. Then, the slidemember 31 is stopped at a stop portion (not shown). Accordingly, thelever member 38 is moved to a position at which the third clutch sectionCL3 becomes the ON state.

As shown in FIG. 33B, only one tooth of the driven gear portion 40 ameshes with the gear portion 25 b. The state is immediately before theend of meshing with the gear portion 25 b. When the driven gear portion40 a is further rotated, the driven toothless portion 40 b faces thegear portion 25 b, the driven gear portion 40 a cannot mesh with thegear portion 25 b, and the driven gear 40 no longer receives the drivingforce from the gear portion 25 b. At this time, if the driven toothlessportion 40 b stops before moving to the position at which the driventoothless portion 40 b completely faces the gear portion 25 b, sound maybe generated by slight collision between the rotating gear portion 25 band a tooth tip of the driven gear portion 40 a. To avoid this, thedriven gear 40 is further rotated without the driving force from thegear portion 25 b. To be specific, the driven gear 40 is rotated bypressing the cam portion 40 c by the elastic force of the torsion spring28 and hence, so that the driven toothless portion 40 b completely facesthe gear portion 25 b and the teeth of the driven gear portion 40 a aresufficiently retracted from the gear portion 25 b in the rotationdirection of the gear portion 25 b. The driven gear 40 is rotated to aposition, at which the driven gear 40 is no longer rotated by thepressure on the cam portion 40 c with the movable arm 28 b due to theelastic force of the torsion spring 28. Accordingly, the fourth clutchdevice B4 becomes the second standby state.

In the second standby state of the fourth clutch device B4, as shown inFIG. 34A, the first slip gear 29, the driven gear 40, and the triggergear 41 are rotated from the state in FIG. 30A by 180 degrees, and thetrigger gear 41 is at the home position. Accordingly, the driven gear 40is also at the home position, at which the driven toothless portion 40 bfaces the gear portion 25 b. The driving force is not transmitted fromthe gear portion 25 b to the trigger gear 41 or the driven gear 40.

Next, as shown in FIG. 34B, the boss 30 c is immediately before the boss30 c contacts the contact portion 31 c of the slide member 31. Similarlyto the state in FIG. 33B, the slide member 31 is stopped at a stopportion (not shown) by the urging force of the slide spring 32 and thelever member 38 is positioned at a second position, at which the thirdclutch section CL3 becomes the ON state. Also, the first gear portion 29c meshes with the second gear portion 30 a of the second slip gear 30.The phase of the second slip gear 30 in which the third clutch sectionCL3 is in the ON state, the trigger gear 41 and the driven gear 40 areat the home positions, and the first gear portion 29 c meshes with thesecond gear portion 30 a is called ON home position (a second stopphase) of the second slip gear 30.

In the drive transmission state shifted from the second standby state ofthe fourth clutch device B4, as shown in FIG. 35A, the solenoid 26 isenergized, hence the retaining claw 26 a is retracted from the retainedportion 41 c, and the retention on the retained portion 41 c by theretaining claw 26 a is released. Then, similarly to FIG. 31A, thetrigger gear 41 rotates first, and then the driven gear 40 starts torotate. By the rotation of the driven gear 40, the first slip gear 29rotates together with the driven gear 40, and the second slip gear 30rotates. Also, while the driven gear 40 meshes with the gear portion 25b and rotates, the cam portion 40 c presses the movable arm 28 b againstthe elastic force of the torsion spring 28, compresses the torsionspring 28, and charges the elastic force.

Also, by the rotation of the second slip gear 30, the boss 30 c contactsthe contact portion 31 c of the slide member 31, and causes the slidemember 31 to make a slide motion in a direction in which the slidespring 32 is compressed against the urging force of the slide spring 32.Accordingly, the slide member 31 turns the lever member 38 to aposition, at which the third clutch section CL3 is changed from the ONstate to the OFF state.

In the drive transmission end state from the drive transmission shiftedfrom the second standby state of the fourth clutch device B4, as shownin FIG. 36A, the driven gear portion 40 a meshes with the gear portion25 b, and the driven gear 40 receives the driving force from the gearportion 25 b and rotates. Also, as shown in FIG. 36B, the retaining claw26 a retains the retained portion 41 c and the rotation of the triggergear 41 is stopped. The trigger gear 41 is at the home position and isat a stop.

The second slip gear 30 rotates until the meshing between the first gearportion 29 c and the second gear portion 30 a is ended and the firstslip portion 29 d faces the second slip portion 30 b. Accordingly, thesecond slip gear 30 does not receive the driving force transmitted fromthe first slip gear 29, which rotates together with the driven gear 40,and the second slip gear 30 is arranged at the OFF home position again.Also, the lever member 38 is moved to the position, at which the thirdclutch section CL3 becomes the OFF state by the boss 30 c and the slidemember 31 is fixed.

In a state immediately before the drive transmission from the drivetransmission shifted from the second standby state of the fourth clutchdevice B4 is ended and the driven gear 40 reaches the home position, asshown in FIG. 37A, the driven gear portion 40 a meshes with only onetooth of the gear portion 25 b. This state is a state immediately beforethe meshing with the gear portion 25 b is ended. When the driven gear 40is further rotated from this state, similarly to FIG. 33B, the driventoothless portion 40 b faces the gear portion 25 b, the driven gearportion 40 a cannot mesh with the gear portion 25 b, and the driven gear40 no longer receives the driving force from the gear portion 25 b.Hence, the driven gear 40 rotates to the home position by causing themovable arm 28 b to press the cam portion 40 c by the elastic force ofthe torsion spring 28.

Also, as shown in FIG. 37B, while the driven gear 40 is rotated to thehome position only by the elastic force of the torsion spring 28, thefirst slip portion 29 d slides on the second slip portion 30 b. Thefirst slip gear 29 rotates without rotating the second slip gear 30,moves to the home position, and stops. Accordingly, the fourth clutchdevice B4 becomes the first standby state shown in FIGS. 30A and 30Bagain. That is, the first slip portion 29 d faces the second slipportion 30 b before a timing, at which the driven gear portion 40 a nolonger meshes with the gear portion 25 b. Accordingly, the first slipportion 29 d slides on the second slip portion 30 b before the timing,at which the driven gear portion 40 a no longer meshes with the gearportion 25 b, and the driving force of the first slip gear 29 is nolonger transmitted to the second slip gear 30.

As described above, in this embodiment, when the second slip gear 30 ismoved to the OFF home position, the slide member 31 is moved to thefirst position against the urging force of the slide spring 32. Incontrast, when the second slip gear 30 is moved to the ON home position,the urging force of the slide spring 32 does not act as a drag when theslide member 31 is moved to the second position. That is, a loadrequired for moving the slide member 31 is larger when the slide member31 is moved to the first position than a load required when the slidemember 31 is moved to the second position. Hence, a rotationalresistance of the second slip gear 30 is the largest when the secondslip gear 30 is moved to the OFF home position. Also, in the fourthclutch device B4, the driven gear 40 cannot obtain the driving forcefrom the gear portion 25 b and the driven gear 40 is rotated only by theelastic force of the torsion spring 28. However, at this time, the firstslip portion 29 d faces the second slip portion 30 b, and the first slipgear 29 is rotatable without rotating the second slip gear 30. Also,when the second slip gear 30 is arranged at the OFF home position, therotation of the second slip gear 30 is restricted even when the secondslip gear 30 receives an external force or the like other than therotational torque from the slide member 31 due to the urging force ofthe slide spring 32.

Hence, the elastic force of the torsion spring 28 that rotates thedriven gear 40 can be set as follows. That is, the elastic force of thetorsion spring 28 can be merely a force that is larger than the totalsum of a force of rotating the driven gear 40 by a predetermined amountagainst the elastic force of the trigger spring 14 when the driven gear40 cannot obtain the driving force from the gear portion 25 b, and arotational resistance force of the first slip gear 29, such as africtional force.

Therefore, the elastic force of the torsion spring 28 being the elasticmember can be decreased, and collision sound which is generated becausethe elastic member collides with the driven rotational body when theelastic member presses the driven rotational body can be decreased.Also, the ease of assembly and workability are less degraded. Also, thetorsion spring 28 being the elastic member constantly contacts andslides on the cam portion 40 c of the driven gear 40 being the drivenrotational body. Hence, by decreasing the elastic force of the torsionspring 28 being the elastic member, the sliding load can be decreased,the driving force required for the drive source (the motor MB) can bedecreased, and the low-output, inexpensive, and compact drive source canbe used.

Also, the rotational resistance received by the second slip gear 30 isthe largest when the second slip gear 30 moves to the OFF home positionby receiving the urging force of the slide spring 32 through the slidemember 31 and the load resistance when the lever member 38 is turned.Hence, the second slip portion 30 b of the second slip gear 30 is formedso that the first slip portion 29 d rotates while sliding on the secondslip portion 30 b when the second slip gear 30 moves to the OFF homeposition. Accordingly, as described above, the elastic force of thetorsion spring 28 can be set at a small force.

In contrast, with the rotational resistance of the second slip gear 30when the second slip gear 30 moves to the ON home position, the boss 30c of the second slip gear 30 does not contact the contact portion 31 cof the slide member 31. Hence, the rotational resistance of the secondslip gear 30 is as large as the rotational sliding load of the secondslip gear 30. The second slip gear 30 is rotatable by the elastic forceof the torsion spring 28 set at the small value as described above.Hence, when the second slip gear 30 moves to the ON home position, theslip portion is not formed at the first slip gear 29 or the second slipgear 30, and the first gear portion 29 c meshes with the second gearportion 30 a.

As described above, in the second slip gear 30, the second slip portion30 b is arranged only at a position, at which the second slip gear 30receives a large rotational resistance (a position serving as the OFFhome position). In the second slip gear 30, the slip portion is notarranged at a position, at which the rotational resistance to bereceived by the second slip gear 30 is relatively small (a positionserving as the ON home position), and the second gear portion 30 a isarranged. That is, among the stop phases in which the second slip gear30 stops (the ON home position, the OFF home position), the slip portion(the second slip portion 30 b) is arranged only in a stop phase with alarge load required when the first slip gear 29 rotates the second slipgear 30. In a stop phase with a relatively small load, the gear portion(the second gear portion 30 a) is arranged. Accordingly, the slipportions (the second slip portions 30 b) can be provided by a minimumnumber. That is, the number of slip portions is smaller than the totalnumber of stop phases in one cycle of the second slip gear. The secondslip portions 30 b each have the size corresponding to 3 teeth of thesecond gear portion 30 a. Hence, by providing the second slip portions30 b by the minimum number, the tooth-number diameter of the second slipgear 30 is not required to be larger than its necessity. Accordingly,the size of the tooth-number diameter of the second slip gear 30 formingthe drive transmission device DR can be decreased.

As described above, with this embodiment, by using the first slip gear29 and the second slip gear 30, the elastic force of the torsion spring28 can be set at a small value. Therefore, similarly to the firstembodiment, the increase in size and cost can be avoided. Also, thesound which is generated because the elastic member collides with thedriven rotational body when the elastic member presses the drivenrotational body, and the sound which is generated because the drivenrotational body rotated by the elastic member collides with theretaining claw can be decreased.

Also, the ease of assembly and workability are less degraded, and thedriving force required for the drive source (the motor M) can bedecreased. Accordingly, a low-output, inexpensive, and small drivesource can be used.

Also, even with the configuration that determines positions of the slidemember 31 being the driven member at a plurality of positions (in aplurality of phases), the second slip portion 30 b is used only when theslide member 31 is at partial positions instead of all positions.Accordingly, the tooth-number diameter of the second slip gear 30 is notrequired to be larger than its necessity. The size of the tooth-numberdiameter of the second slip gear 30 forming the drive transmissiondevice DR can be decreased.

The slide member 31 being the driven member linearly moves in areciprocating manner by the second slip gear 30. However, the drivenmember is not limited thereto. That is, the driven member can havemerely a case of a relatively large moving load and a case of arelatively small moving load depending on the phase. The movement of thedriven member can be rotation, or one-direction movement instead ofreciprocation.

The configuration in which the slip portion is provided only in partialstop phases among the stop phases and the gear portion is provided inthe other stop phase like the fourth clutch device B4 of theabove-described embodiment can be applied to a configuration similar toany of the first to third clutch devices B1 to B3 described in the firstto third embodiments.

With the invention, the elastic force of the elastic member required forrotating the driven rotational body can be decreased.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

The invention claimed is:
 1. A drive transmission device including adriving rotational body, a driven rotational body that rotates byengaging with the driving rotational body, a driven member that isdriven by the rotation of the driven rotational body, and an elasticmember that rotates the driven rotational body by an elastic force whenthe driven rotational body does not engage with the driving rotationalbody, the drive transmission device comprising: a first rotational bodyand a second rotational body arranged downstream of the drivenrotational body in a drive train that transmits a driving force from thedriving rotational body to the driven member, the first rotational bodybeing configured to rotate in synchronization with the driven rotationalbody, the second rotational body being configured to be rotated by thefirst rotational body and drive the driven member, wherein, when thedriven rotational body rotates by the elastic force of the elasticmember, a case in which the first rotational body rotates withoutrotating the second rotational body, and a case in which the firstrotational body rotates while rotating the second rotational body areprovided, wherein the driven member can move to a first position and asecond position as a result that the driven member is driven by thesecond rotational body and moves, and a load required for the drivenmember to move is larger when the driven member is displaced to thefirst position than a load required when the driven member is displacedto the second position, and wherein the first rotational body rotateswithout rotating the second rotational body by the elastic force of theelastic member when the driven member is at the first position, and thefirst rotational body rotates while rotating the second rotational bodyby the elastic force of the elastic member when the driven member is atthe second position.
 2. The drive transmission device according to claim1, wherein the first rotational body rotates the second rotational bodywhen the driven rotational body engages with the driving rotational bodyand rotates.
 3. The drive transmission device according to claim 1,wherein the first rotational body and the second rotational body aregears that mesh with each other, and wherein a gear portion is notformed in a portion of the first rotational body that faces the secondrotational body in a phase in which the first rotational body does notrotate the second rotational body, and a gear portion is formed in aportion of the first rotational body that faces the first rotationalbody in a phase in which the first rotational body rotates the secondrotational body.
 4. The drive transmission device according to claim 3,wherein the number of teeth of the second rotational body is smallerthan the number of teeth of the first rotational body by one tooth. 5.The drive transmission device according to claim 1, wherein the firstrotational body and the second rotational body are gears that mesh witheach other, and wherein a gear portion is not formed in a portion of thesecond rotational body that faces the first rotational body in a phasein which the first rotational body does not rotate the second rotationalbody, and a gear portion is formed in a portion of the second rotationalbody that faces the first rotational body in a phase in which the firstrotational body rotates the second rotational body.
 6. The drivetransmission device according to claim 1, wherein an arcuate surfacecoaxial with a rotation center of the first rotational body is providedin a portion of the first rotational body that faces the secondrotational body in a phase in which the first rotational body does notrotate the second rotational body, and an arcuate surface extendingalong the arcuate surface of the first rotational body is provided in aportion of the second rotational body that faces the first rotationalbody in the phase in which the first rotational body does not rotate thesecond rotational body.
 7. The drive transmission device according toclaim 6, wherein the arcuate surface of the second rotational bodyincludes a plurality of arcuate surfaces.
 8. The drive transmissiondevice according to claim 1, wherein the driving rotational body and thedriven rotational body are gears that mesh and engage with each other,and the driven rotational body has a portion that does not have a gearportion and does not mesh with the driving rotational body.
 9. The drivetransmission device according to claim 1, wherein the driven rotationalbody is rotated to a position, at which the engagement between thedriven rotational body and the driving rotational body is completelyreleased, by the elastic force of the elastic member.
 10. The drivetransmission device according to claim 1, further comprising: anotherdriven rotational body that rotates coaxially with the driven rotationalbody by engaging with the driving rotational body; and another elasticmember provided between the driven rotational body and the other drivenrotational body, wherein the driven rotational body is rotated to aposition, at which the engagement between the driven rotational body andthe driving rotational body is completely released, by the elastic forceof the elastic member against an urging force of the other elasticmember.
 11. An image forming apparatus comprising: the drivetransmission device according to claim 1; a developing member thatcauses a toner to adhere to an image bearing body; and a drive sourcethat rotates the developing member, wherein a driving force from thedrive source is not transmitted to the developing member when the drivenmember of the drive transmission device is at the first position, andthe driving force from the drive source is transmitted to the developingmember and the developing member rotates when the driven member of thedrive transmission device is at the second position.
 12. A drivetransmission device including a driving rotational body, a drivenrotational body that rotates by engaging with the driving rotationalbody, a driven member that is driven by the rotation of the drivenrotational body, and an elastic member that rotates the drivenrotational body by an elastic force when the driven rotational body doesnot engage with the driving rotational body, the drive transmissiondevice comprising: a first rotational body and a second rotational bodyarranged downstream of the driven rotational body in a drive train thattransmits a driving force from the driving rotational body to the drivenmember, the first rotational body being configured to rotate insynchronization with the driven rotational body, the second rotationalbody being configured to be rotated by the first rotational body anddrive the driven member, another driven rotational body that rotatescoaxially with the driven rotational body by engaging with the drivingrotational body; and another elastic member provided between the drivenrotational body and the other driven rotational body; wherein, when thedriven rotational body rotates by the elastic force of the elasticmember, a case in which the first rotational body rotates withoutrotating the second rotational body, and a case in which the firstrotational body rotates while rotating the second rotational body areprovided, and wherein the driven rotational body is rotated to aposition, at which the engagement between the driven rotational body andthe driving rotational body is completely released, by the elastic forceof the elastic member against an urging force of the another elasticmember.
 13. An image forming apparatus comprising: the drivetransmission device according to claim 12; a developing member thatcauses a toner to adhere to an image bearing body; and a drive sourcethat rotates the developing member, wherein the driven member can moveto a first position and a second position as a result that the drivenmember is driven by the second rotational body and moves, and a loadrequired for the driven member to move is larger when the driven memberis displaced to the first position than a load required when the drivenmember is displaced to the second position, wherein the first rotationalbody rotates without rotating the second rotational body by the elasticforce of the elastic member when the driven member is at the firstposition, and the first rotational body rotates while rotating thesecond rotational body by the elastic force of the elastic member whenthe driven member is at the second position, and wherein a driving forcefrom the drive source is not transmitted to the developing member whenthe driven member of the drive transmission device is at the firstposition, and the driving force from the drive source is transmitted tothe developing member and the developing member rotates when the drivenmember of the drive transmission device is at the second position.